Weather456's Tropical Weather Blog

June Tropical Weather Outlook

By: Weather456, 11:16 AM GMT on May 31, 2010

The 2010 Atlantic Hurricane Season begins tomorrow!

2010 Hurricane Season Names


Introduction

The beginning of the hurricane season is most closely related to the timing of increases in sea surface temperatures, convective instability, and other thermodynamic factors. Although this month marks the beginning of the hurricane season, the month of June generally sees little activity, with an average of about 1 tropical cyclone every 2 years. Tropical systems usually form in the Northwestern Caribbean Sea, Gulf of Mexico or off the east coast of the United States.

Since 1851, a total of 81 tropical storms and hurricanes have formed in the month of June. During this period, two of these systems developed in the deep tropics. Since 1870, three major hurricanes have formed during the month, the most notable of which was Category 4 Hurricane Audrey in 1957. Audrey is the earliest forming Category 4 hurricane in the basin and for 48 years, Before Hurricanes Dennis and Emily of 2005, the latter a Category five hurricane, it was the strongest pre-August tropical cyclone. The easternmost forming storm during June was Tropical Storm Ana in 1979, forming at 45W.

I am expecting a moderate chance that June 2010 will be above the long-term mean.


Figure 1. Track of all tropical cyclones occuring in June between 1851 and 2006 showing the majority of storms were clustered and tracked in the Western Caribbean and Gulf of Mexico.

Main Indicators

- El Nino Southern Oscillation and Vertical Shear Relationship
- Intraseasonal Rainfall Patterns
- Sea Surface Temperatures and Tropical Heat
- Steering Flow
- The TUTT and Mean Sea Level Pressure

The El Nino Southern Oscillation (ENSO) and Vertical Shear Relationship

It is has been known that El Nino is no more and that neutral conditions and possibly the onset of La Nina is now underway. During El Nino events, the 200 mb winds emanating from the Pacific creates abnormally high levels of shear over the Caribbean and Western Atlantic. The opposite occurs in neutral and La Nina events where the 200 mb flow are easterly, in the same direction as the surface easterlies, thus the shear magnitude is much lower in said years. During the last two weeks of May, vertical shear overall has been lower than normal across the Atlantic, likely in response to the weakened El Nino. The main development regions for June – the Caribbean and Gulf of Mexico continue to see near average to below normal shear with the greatest anomalies in the Caribbean Basin.

These conditions are expected throughout the month of June as leading climate models continue to foresee the cooling of the tropical equatorial Pacific. There is almost a 90% chance of continued neutral conditions with a 10% that La Nina conditions will develop by month’s end. In response to this, the medium range model – Global Forecasting System (GFS) – indicate that our subtropical jet which created high levels of shear over the Gulf during late May into early next month, will weaken by mid-June, though lingering effects will be noticeable. Further out in time, the Climate Forecast Model (CFS) foresees below normal shear over the Caribbean but near-above normal shear over the Gulf of Mexico. This model strikes me as unstable since these were not exactly what was forecasted just two weeks ago. Given these parameters, I would say vertical shear should be in favour of cyclogenesis this month, mainly in the Caribbean.


Figure 2. Climate Forecast System (CFS) NINO 4 SST anomaly forecast showing neutral conditions for much of June with continued cooling leading to La Nina later this summer.


Figure 3. GFS Wind shear forecast through 15 June 2010 showing an overview of the pattern expected with lingering shear near the subtropical jet giving way to periods of low and high shear over the Gulf of Mexico, while low shear remains over the Caribbean Basin. Also notice the TUTT cell over Cuba.


Intraseasonal Rainfall Patterns

When we speak of intraseasonal, we are referring to a timescale smaller than seasonal. In this case, the intraseasonal rainfall modulator is the Madden-Julian Oscillation (MJO). We can expect a higher chance of development during the MJO upward phase and a lower, but not zero, chance of development in the downward phase. During the last week and half, the upward phase of the MJO visited the Western Atlantic leading to very convective events. This upward pulse is expected to last through the first week of June and then transition to the downward pulse by mid-June. Thus, the chances of seeing convective activity lower as the month progresses with the next upward pulse expected late in the month. In the meantime, the Climate Prediction Centre’s tropical risk assessment anticipates an increase chance in cyclogenesis in the first week of June due to below normal shear and increase in convective activity.


Sea Surface Temperatures and Tropical Heat

Why bother discuss this factor? Record sea surface temperatures and atmospheric heat are headlines in the meteorological community. April was the warmest on record globally according to the Climate Prediction Center and the Atlantic was one of the two places where the heat was highest. Though sea surface temperature anomalies have lowered over the past two weeks, there remains few areas in the tropical Atlantic or main development region (MDR) that cannot support a tropical storm or hurricane. Currently, the highest ocean heat content is locked up in the Western Caribbean, a favoured area for June and sea surface temperatures remain at 2005 levels. Global blended SST forecasts continue to forecast warm anomalies as high as 1-2C over the main development region with cool anomalies expected over the Gulf of Mexico.


Figure 4. Sea surface temperatures on May 29 for both 2010 and 2005 showing nearly similar levels.

Steering Flow

The western Atlantic remains in a pattern of alternating troughs and ridges and this is expected to continue into June. However, there is more broad-scale troughing than ridging, typical of June. Thus, anything forming in the Gulf or Western Caribbean will tend to follow climatological tracks and affect areas around the Northwestern Caribbean, the Northeastern Gulf Coast and East Coast.


Figure 5. Forecast of the location where the 500 mb pressure surface will be at a height of 582 decameters (5280 meters) above sea level based on the GFS. This height is where storm tracks are affected the most.

Other Factors

There are indications based on the GFS 200 mb analysis that the Tropical Upper Tropospheric Trough (TUTT) will begin to establish itself across the Western Atlantic. Long-range GFS animations revealed upper level secluded lows moving east to west south of 30N by mid-month suggestive of TUTT cells. The TUTT’s position relative to the Northwest Caribbean should provide a favourable upper level outflow pattern for developing systems.

Mean sea level pressure was below normal throughout the main development region, but closer to normal in the Western Caribbean. Given that mean sea level pressure is affected by the amount of upward or downward force in the atmosphere, continued upward force due to warm sea surface temperature temperatures and a favourable MJO should continue to result in below normal sea level pressure across the Western Atlantic, which favours cyclogenesis.

Summary

There is a slight distinction between the two main areas of June tropical storm formation – The Gulf of Mexico and the Western Caribbean. The Gulf of Mexico is expected to become a bit more favourable but not optimal for tropical cyclone formation due to the lingering effects of a weakening subtropical jet stream and below-near normal sea surface temperatures. The Western Caribbean on the other hand, has a greater chance of seeing cyclogenesis due to increase in convective activity, reduce shear, below normal mean sea level pressures and above normal sea surface temperatures. Climatology states that there is a 50% chance of seeing a named storm in June and based on the given conditions, there is a moderate chance of being above this mean. There is a moderate-high chance of cyclogenesis, if any, occurring in the Northwestern Caribbean, with a low-moderate chance of it occurring in the Gulf of Mexico.


Figure 6. Composite summary of what to expect entering the hurricane season of 2010 with region A representing favorable conditions over the NW Caribbean and region B, marginally favorable areas over the Gulf of Mexico. Areas affected by any system forming this month are given in color codes, with yellow - low, pink - medium and red - high. The prevailing tracks given by white arrows and the subtropical jet stream is indicated by the three-lined flow. There is a trough along the east coast to represent broad scale troughing while the TUTT is seen as the blue dashed line with TUTT cells embedded. The subequatorial ridge centers are given by "H" with the ridge crest, the blue lines.

My July outlook would seek to expand on the tropical Atlantic since that is when I expect the season to really begin to show its true colours.

Other Reads

2010 Hurricane Season Outlook
May 15-31 Tropical Weather Outlook

Tropical Update

The remnants of Tropical Storm Agatha are over the Northwestern Caribbean Sea, more specifically right along the coast of Belize. This was based on vorticity maps; circulation charts, shortwave infrared imagery and surface observations, which all agreed that the mid-low level remains of Agatha are just hugging the coast remaining quasi stationary. Currently the system is located in weak steering flow, but should begin a gradual motion towards the north-northeast over the next day or two. Conditions in the northwest Caribbean will be somewhat favourable for redevelopment of Agatha but that remains a small window of opportunity considering hostile conditions await in the Gulf of Mexico over the next 3-5 days. Nevertheless, I will continue to monitor the progress of this system as this morning satellite imagery showed thunderstorms forming offshore which in these cases can cause center relocations. I give this a low chance of redeveloping over the next day based on the given conditions and the lack of model support. Regardless of development, some level moisture will spread over the Caymans, Western Cuba and the Southern portion of Florida over the next 3-4 days.

Agatha became the wettest cyclone to affect the country of Guatemala, surpassing Mitch of 1998. This huge amount of rainfall mixed with ash, rock and soil led to major flooding, landslides and mudslides and the death toll now stands at 83 in the country and more than 100 across Central America. It is really sad because this is the stuff that was forecasted but sometimes you wished that these forecast would actually in turn help reduce the cost of lives. It could of been much worst had persons not evacuated during the eruption on Thursday and Friday of Guatemala's Pacaya volcano.

Weather456

Agatha floods Central America

By: Weather456, 11:58 AM GMT on May 30, 2010

The first tropical storm of the Eastern Pacific made landfall yesterday afternoon near the Mexican/Guatemalan border and continued to dump tremendous amount of rains across parts of Central America. According to the Guatemala's meteorological institute, about 12 inches of rain fell in the past 30 hrs near the community of Champerico. This heavy rain was mixed with ash from the eruption of Pacaya, boulders and soil to create mudslides and landslides, which killed 12 in Guatemala and 2 in nearby El Salvador and Nicaragua. These mudslides also destroyed over 800 homes. The cement-like substance also clogged up drainage systems and led to even more flooding. The president of the country most affected – Guatemala, declared a state of emergency in wake of the twin-natural disasters and compared this storm to that of Mitch in 1998 and Stan in 2005.

Current Information

The National Hurricane Center issued their last advisory on Agatha this morning citing the surface circulation has dissipated. However, satellite imagery and vorticity maps at CIMSS showed that the mid-level energy remains intact since the mountains over the region only extend to about 700 mb the most. Based on these estimates, the center is almost near the Guatemala and Belize border. Satellite imagery also showed that while the system has dissipated, it continues to dumped heavy rains over the area, which will likely lead to further flooding. Reports from government officials stated, “The worst of Agatha's impact is yet to be recognized.”


Figure 1. Funktop infrared channel of Agatha taken this morning at 06:45am EDT. Funktop enhancement assists in precipitation analysis.

Rainfall Estimates

Due to the sparse observations network in the country of Guatemala, it will be somewhat difficult to get a handle on the amount of precipitation that fell, especially in the isolated mountain hillsides. However, satellite estimates can help fill this void. Rainfall estimates from passive microwave imagers showed 7-10 inches of rain fell over the country in the past 24 hrs. Since satellite estimates do understate rainfall in extreme cases like tropical cyclones – it is likely that actual rainfall accumulations were higher. NASA’s TRMM satellite estimated that 20-25 inches of rain fell just along the coast from the storm over the past week. This is about 80 855 tons of water up until Thursday.


Figure 2. Blended IR & Passive Microwave (PMW) 24-hr rainfall accumulation ending 2:00am EDT this morning.

Numerical model predictions expect another 5-10 inches of rain to fall over the affected areas as Agatha continues inland with smaller accumulations over Belize the Mexican Yucatan. According to the Belize National Weather Service Doppler radar, it has been steadily raining over the country since yesterday evening, which is located at the leading edge of Agatha’s rain bands.


Figure 3. Ensemble Tropical Rainfall Potential (eTRaP) expected rainfall accumulation in 6-12 hrs valid from 2:00am EDT this morning.

Future

Agatha is a very slow moving system so the effects of the storm will continue to slow relief efforts and exaggerate the disaster even further. The government of Guatemala is already seeking an 85 million dollar loan to help cope with the disasters.

Numerical models are showing that Agatha will emerge either over the extreme Western Caribbean or Southern Gulf of Mexico in about 36-48 hrs. Such a long duration over land, decreases the chances of Agatha re-organizing into a system on the Atlantic side. Furthermore, vertical shear is only marginally favourable at best over the NW Caribbean and extremely unfavourable over the Gulf of Mexico. However, models continue to show some level of moisture reaching the Florida Peninsula by mid-week. I expect about 1-4 inches over the state from ex-Agatha but highly doubt any significant reorganization of the system.

A Little Math

In one week, the total rainfall from 90E was about 80 855 tons of water. Most of it fell in the Pacific Ocean. How did I arrive at this figure?

Well the surface precipitation rate over the past week was about 0.00027 kg per second, and since there are 604 800 seconds in a week, that is about 163 kilograms of precipitation in one week. However, that is just the amount for one square meter. The area affected by 90E is 450 000 m^2 for a total of 73 350 000 kilograms of precipitation.


Figure 4. 7-day mean surface precipitation rate in kg/m^2/s. Image credit: NOAA's Physical Sciences Division.

Weather456

90E nears depression status; heavy rains expected

By: Weather456, 12:14 PM GMT on May 29, 2010


Figure 1. GOES infrared image of tropical disturbance 90E, taken 29 May 2010 at 7:15am EDT.

Tropical Invest 90E is estimated to be located near 14N-93.5W, moving slowly off towards the east-northeast. Estimated surface winds are near 35 mph with a minimum central pressure of 1004 millibars. The center of 90E was easily located using microwave imagery, an ASCAT pass from earlier this morning and satellite imagery. Invest 90E has continued to show signs of organization and satellite presentations continue to improve. The center is located just at the edge of the deepest circular area of convection due to the shear gradient just to the north of 90E, which has been tugging on 90E over the past day or two. Nevertheless, microwave imagery revealed a well-define center and along with the ASCAT pass and Dvorak estimates, winds at the surface may have already reached tropical depression force. Although environmental conditions appear conducive for the further organization of 90E, proximity to land should limit intensity, which may be offset by 90E’s slow motion – that is weather for you. Most of the intensity guidance insists that 90E will not make it to tropical storm status before landfall, which is reasonable, but given the current organization of 90E, it cannot be ruled out. My thinking is that the disturbance has a moderate-high chance of becoming a tropical depression, and possibly a tropical storm before landfall. It is unlikely that 90E will be a significant system in terms of wind before landfall.

90E has steadily moved eastward over the past day or two under the influence of deep layer westerlies and troughing to the north. This motion is expected to continue upon until landfall in 2-3 days. In about 4 days, high pressure builds over the SW Atlantic and the mid-shallow flow takes whatever is left of 90E more towards the north and possibly into the Gulf of Mexico. Environmental conditions in the Gulf of Mexico are very unfavourable for the development of any remnants that may survive the terrain of Central America and the reliable models reflect this. The CMC seems to indicate a shortwave will amplify 90E into a significant system and impact Florida, which is highly unlikely. Expect some level of moisture in the Gulf of Mexico from the remnants of 90E through 5 days.

The slow movement of 90E will prove detrimental to parts of Central America due to the concern of flooding. The disturbance has been sitting offshore for several days now and not expected to make landfall for another one, possibly 2-3 days. Satellite rainfall estimates indicate rain rates between 0.5-1” per hour and accumulations over the past 12 hrs have been around 4-6 inches. Thankfully, much of the heavier rain rates remain offshore but that may not serve to prevent flooding in already saturated soils.


Figure 2. AMSRE passes of 90E from 3am EDT this morning showing wind and rainfall estimates of the disturbance. The wind estimates maybe off due to cloud cover, which is why my wind estimate used was closer to the ASCAT pass than the microwave overpasses. However, it does show the circulation well.

Guatemala's Pacaya Volcano

Guatemala's Pacaya volcano started erupting lava and rocks Thursday afternoon, blanketing the country's capital with ash and forcing the closure of the international airport. In Guatemala, the ash billowing from Pacaya has been thick and falls quickly to the ground, unlike the lighter ash that spewed from the volcano in Iceland and swept over much of Europe, disrupting global air travel, said Gustavo Chigna, a volcano expert with Guatemala's institute of seismology and volcanoes. According to the Jarkata Post, in Guatemala, at least 1,910 people from villages closest to the Pacaya volcano were moved to shelters. Some 800 homes were damaged in the initial eruption late Thursday. A second eruption at midday Friday released ash in smaller amounts from the 8,373-foot (2,552 meter) mountain.

It seems rather unfortunate that this eruption is succeeded by the potential landfall of a tropical system, which is dumping heavy rains across the country. This rainfall mixed with the thick ash further increases the chances of mudslides as the volcano is located right in the heaviest rainfall zone of 90E.

The ash has since then spread east into Honduras and is expected to reach the Caribbean Sea in 2-3 days. Interestingly enough, the ash column was difficult to detect via satellite imagery due to the clouds from the disturbance but ground observations indicate an ash plume 800 meters above the dome.


Figure 3. Infrared imagery of 90E with GFS rain rates overlaid and the location of the volcano and current ash deposits.

The Caribbean

A plume of moisture continues to lift out of the Caribbean after dumping several inches from Jamaica to the Leeward Islands. Both personal and official weather stations reported between 1-8 inches across the islands, with the heaviest in Puerto Rico. Most islands reported some level of flooding. Expect another 1-3 inches as the moisture plume lifts out over the next 3 days.

Weather456

90E and the Caribbean

By: Weather456, 10:56 AM GMT on May 28, 2010

The center of 90E is estimated to be located near 12N/96W, drifting off towards the north. Estimated surface winds are near 30 mph with a minimum central pressure of 1000 millibars. The center of 90E was very difficult to located so it should be noted that it might also be located further northeast near 13N/95W based on shortwave infrared imagery. It is rather unclear if this low-level center is closed but a recent ASCAT pass indicate it may be so, to some extent. Satellite appearance of 90E has improved during the overnight hours with intense bands of convection in and around the center. Over the past 24 hrs, the system appears to be struggling with its size, trying to consolidate into a central point, with waning and waxing during the diurnal cycle. The system however, appears smaller this morning, which is indicative of development and an increase in the Dvorak T# from “TOO WEAK” to 1.0 lend support to this. The current intensity of 90E is comparable to the physics of an ice skater. The broad circulation spins slower just as an ice skater stretches out his/her hand to slow down. As the circulation becomes tighter, the winds spin faster just as an ice skater pulls in her hand to spin faster. Conditions appear conducive for the further development and tightening of this circulation and I give 90E, a moderate chance of becoming the Eastern Pacific’s first depression. The other possibility is that 90E just rains itself out over Central America without being named.

Currently, 90E’s movement towards the north is a direct result of the tugging force by the upper trough associated with ex-90L, which penetrates even to the shallow layers, and a deep layer ridge over Northern Mexico. This pattern should continue over the next few days bringing 90E closer to the Central American coast in 2-5 days. Models differ greatly on timing and with the slow movement of 90E, uncertainty is great. The biggest impact from 90E, regardless of classification is going to be its rains. Satellite rainfall estimates have already indicated that 90E has dumped close 4-5 inches in just 24 hrs over parts of Central America and another 3-5 inches per day expected by the GFS. Total rainfall over the past week, which encompasses the precursor of 90E and 90E itself, is 12 inches. These tropical rains could cause flooding and landslide dangers along the west coast.


Figure 1. Blended IR & Passive Microwave (PMW) Rain Accumulation for 1 week ending 8:00pm EDT May 26 2010.

The Caribbean

The Caribbean basin remains very convective this morning with several areas of interest. First, broad upper troughing has continued to produce a plume of moisture extending from the ITCZ across the Eastern Caribbean and into the Atlantic inducing showers and thunderstorms over Hispaniola, Puerto Rico, the Virgin Islands and the Leeward Islands. Expect this activity to continue over the next 36-48 hrs with 1-3 inches and isolated amounts of 3-5 inches.

The other area of interest is a disturbance sitting offshore the Nicaragua/Honduras border, which appears to be some of the energy from the formation of 90E. This disturbance has gotten a bit convective this morning and most of the global models with the exception of the ECMWF are developing this feature into a weak depression as it moves off towards the northeast or east-northeast. Conditions are only marginally favourable for development with wind shear bordering 20 knots and not expected to change much over the next 72 hrs. In addition, the circulation remains poor and there are no indications of falling pressure as of yet. Nevertheless, the models seem to indicate with consensus, of cyclogenesis, so the area will be monitored. Meanwhile, heavy rains are going to spread over Jamaica over the next 24-48 hrs, with the island picking up as much as 5 inches.


Figure 2. Water vapor imagery of the Western Atlantic basin with the shallow-mid level steering (yellow lines) and upper layer flow (red arrows) overlaid. Notice this type of pattern favors the northeastward motion of both 90E and the area of interest (AOI) over the NW Caribbean Sea. Also notice, the fast upper winds at the boundary of the latter disturbance indicating marginally favorable upper environment for development.

Weather456

90L fades away while 90E develops

By: Weather456, 11:37 AM GMT on May 27, 2010

Invest ex-90L continues to churn over the southwest Atlantic and while the circulation has gotten much more define over the past 24 hrs, this feature remains void of any deep convection and no further development is expected of the system. Currently, the system is enveloped within a very broad upper trough digging from Eastern Canada, helping the system to slowly move off towards the east. This motion should continue over the next 24-48 hrs and the system should weaken as upper level forcing does. However, most models are showing that ex-90L will not entirely absorb as high pressure quickly builds in behind the trough and forces ex-90L or some of its energy back towards the west. This scenario is feasible but the likelihood of ex-90L redeveloping is very slim since conditions would not be the same as when the system was first developing. The low will likely dissipate before reaching land, if it does retrograde back west. Breezy conditions accompanied by 5-10 ft seas could affect Bermuda as the system nears their vicinity once more.

The development of a warm-core feature, highest winds near the define center of circulation and capped by an upper level circulation led this forecaster to believe 90L was not entirely non-tropical. It was certainly not tropical; therefore, we are left to assume it was subtropical. However, AMSU temperature cross section showed the warm core was located in the upper troposphere with cool anomalies in the mid-troposphere. Such a vertical temperature profile is indicative of cold dry air advection into the system at the mid-levels thus retarding any significant thunderstorms. Thus, despite the system having subtropical characteristics, it was not organized enough to be designated a subtropical depression or subtropical storm.

This is the last forecast on 90L unless something warrants.


Figure 1. NASA's MODIS TERRA captured this image of 90L yesterday showing satellite presentations not common in extratropical or tropical cyclones but rather hybrids. Satellite imagery is just one of the objective data which supports the theory that 90L was subtropical or hybrid.

Tropical Invest 90E

Invest 90E was estimated to be located near 12.5N-94.5W, remaining stationary. Estimated surface winds are near 30mph with a minimum central pressure of 1006 millibars. The center fix was based on shortwave infrared imagery, an ASCAT pass from early this morning and multiplatform satellite winds. Satellite imagery revealed that 90E has organized a great deal overnight with clear curvature (banding) of very deep convection indicating the centre’s position. The system is moving over 30C waters and excellent outflow is evident aloft. These conditions appear conducive for the continued organization of 90E as it heads off towards north-northwest over the next day or two. This motion maybe short-lived as the same upper trough associated with 90L has dug deep enough across the area to tug 90E north then northeast into Southeast Mexico, Guatemala or El Salvador. This may shorten the time 90E has to organize and intensify and it may end up reaching, at most, a category 1 storm before making landfall. Regardless of development, heavy rains will spread across parts of Central America over the next 5-7 days, possibly delivering over 15 inches of rain and increasing the likelihood of floods and landslides.

Some of the models continue to indicate that some of the energy associated with 90E will cross over into the Caribbean Sea and develop into a depression. Conditions in the Northwest Caribbean will be marginally conducive to support this scenario, as the subtropical jet stream will be near 20N. Such as system would be steered northeast under the influence of the very same upper trough.

Heavy rains will continue to spread over Hispaniola, Puerto Rico and the Leeward Islands later today and over the next day or two as an upper trough over the Central Caribbean continues to enhance showers and thunderstorms over these areas. Some of these areas could pick up 3-6 inches over the next couple of days.


Figure 2. Water vapor imagery of the entire North Atlantic showing an overview of several features discussed in today's update.


Other news

The National Oceanic Atmospheric Administration (NOAA) will be issuing their 2010 hurricane season outlook around 10am this morning and it is something that I think most forecasters in the tropical meteorology community is looking forward to. I will post my thoughts on their outlook either tomorrow or sometime on the weekend.

My June outlook is schedule for Monday.

Weather456

Tropical Update - 90L, 90E and the Caribbean

By: Weather456, 10:05 AM GMT on May 26, 2010

Tropical Invest 90L continues to churn over the Southwest Atlantic bringing breezy winds, rain and surf to the Southeast Coast. Satellite imagery estimated the center to be near 31N-76W, moving off towards the southwest. Estimated winds are near 40 knots and minimum central pressure is around 1007 millibars. Satellite presentations of 90L have improved over the past 24 hrs, with deep convection in and around the low-level center, which remains rather broad. Nevertheless, further satellite analysis revealed 90L was able to take some advantage of the Gulf Stream and generate enough convection to produce a warm-core aloft. Furthermore, ASCAT and AMSU passes from last night revealed the maximum winds of 30-40 knots were displaced about 500 miles away from the center. Based on the given data and evidence, 90L could not have been tropical or non-tropical. It is my thinking that 90L is subtropical but not organized enough to be named. The disturbance has about 24-48 hrs left in the vicinity and thus a small window of opportunity remains open for 90L before a trough over Eastern Canada digs across the area and begins to absorbed 90L by Friday.

Regardless of classification, the disturbance produced gale force conditions offshore the Southeast Coast with the majority of buoys reporting peak gusts of 30 knots. Winds ashore were much less, around 15-20 knots and seas measured 10-15 ft. Rainfall totals were around 1 inch over north Carolina over the past day (almost 4 inches since Sunday from an unrelated system), but the heaviest rainfall from 90L fell in South Carolina where areas picked up 1-3 inches. Some of these areas can expect another half inch as 90L slowly pulls away from the coast over the next day or two.


Figure 1. The Advance Hydrologic Prediction Service (AHPS) Southeast United States current 1-day observed precipitation valid 11:43pm EDT 25 May 2010.

Invest 90E, Central America and the Caribbean

A broad area of disturbed weather located in the Eastern Pacific has the potential to become the Eastern Pacific’s first named storm. Satellite imagery showed intense convection related to this feature. Vertical shear is about 10-15 knots over the disturbance, outflow is established aloft with sea surface temperatures near 30C and plenty of ocean heat to work with. Thus, the potential for this storm to become a tropical storm is high. The system, once formed, will likely parallel the coast before making landfall near southeast Mexico or Guatemala in about 3 days. Some of the models are showing that a piece of this energy will break off and head into the Northwestern Caribbean to become a depression there. While the models this morning are less enthusiastic of this scenario, it is feasible and conditions in the Northwest Caribbean in 4-7 days appear conducive. Thus, it will be monitored. Regardless of development, heavy rains, possibly life threatening, will occur along the Pacific slopes of Central America from Mexico to Costa Rica. Model expected rainfall amounts in 5 days exceed 15 inches.

Another area of disturbed weather lies in the Caribbean Sea where an upper trough of low pressure is enhancing showers stretching from the ITCZ across the Central Caribbean, Jamaica, Hispaniola and Puerto Rico. Some of these areas could pick up around 3-5 inches of rain over the next couple of days as the trough slowly lifts out.


Figure 2. Water vapor imagery of the Western Atlantic, Caribbean Sea and Eastern Pacific showing an overview of several features discussed today. Notice the outflow pattern over 90E which is being enhanced by the upper trough over the Caribbean which in turn is enhancing showers over the central Caribbean.

Other News

My June Outlook will be issued on Monday 31 May 2010.

Weather456

Little change to 90L as it heads towards the Carolinas; Central America flood threat

By: Weather456, 11:19 AM GMT on May 25, 2010

Invest 90L

There has been little change to the non-tropical area of disorganized showers and thunderstorms over the Southwest Atlantic as it continues off towards the northwest. Satellite imagery showed the center of circulation to be located near 29.9N-72.5W moving off towards the northwest. Estimated winds are near 45 mph with a minimum central pressure of 1007 millibars. Much of the convection remains on the northern side of the center, not due to wind shear but rather dry air intrusion. In fact, there are hints of thunderstorms building near the center but the feature remains disorganize and has changed little over the past 24 hrs. This may change as the system is heading for warmer waters of 25C-26C near the Gulf Stream and lower shear. It is also becoming more vertically stacked as it creeps under the mid-upper level circulations. Thus, there is still a small window of opportunity left for 90L to become subtropical before being absorbed later this week.

Expect the system to continue to move in a northwesterly direction towards the southeast coast over the next 3 days under the influence bridging high pressure over the Northeastern United States. Afterwhich, a strong frontal trough will dig deep from Eastern Canada and break down the ridge bridge (no pun intended) and lift 90L off towards the northeast.

Regardless of designation, 90L will continue generate gale force winds and rough surf to the north of the circulation. Buoy 41048 reported peak wind gusts of 45 knots and wave heights of 18 ft, which verified the forecast. The Civil Air Terminal in Bermuda picked up half an inch of rain between yesterday and today and reported peak wind speeds of 30 mph at 5:55am EDT this morning. These conditions should reach the Carolinas later today and on Wednesday with the threats of rip currents, minor beach erosion and flooding and a chance of rain increasing. These conditions should subside through Thursday and Friday.


Figure 1. RTMA surface wind analysis of 90L around 6:00am EDT this morning with surface observations overlaid. The green and yellow shadings indicate winds of 30-50 mph. These should reach the coast later today and tomorrow.

Central America under threat of flooding

Heavy rains associated with a broad area of low pressure and a series of tropical waves have dumped an estimated 4-7 inches of rain over parts of Central America over the past 3 days, with potentially another 3-7 inches expected over the next 24 hrs especially along the Pacific slopes of Costa Rica and Nicaragua. As a result, NASA’s TRMM satellite flood potential has increased for these parts. Most of the global models are hinting that either an area of low pressure will form in the Eastern Pacific or over Central America itself, and move towards the north into the Gulf of Honduras due to the effects of the frontal trough that will absorbed 90L. Most of the reliable models show conditions improving over the Northwest Caribbean by weekend but the ECMWF shows a cyclone forming in the Eastern Pacific and making landfall near Guatemala but never re-forming over the Caribbean as shown by the majority of models. Nevertheless, the area will be monitored for development and such a system would affect the Caymans, Cuba and/or Jamaica. Meanwhile, heavy rains will continue over the region, increasing the threat of flooding. This situation reminds of Alma-Arthur back in 2008 but instead of Arthur moving west back into Central America, this feature would move northeast due to weakness in the subtropical ridge.


Figure 2. 3-day passive microwave (PMW) rain accumulation ending 00Z May 24 2010.


Weather456

Code orange for 90L; Bermuda to get rains, gusty winds and rough seas

By: Weather456, 11:19 AM GMT on May 24, 2010

Non-tropical invest 90L continues to produce a very large area of disorganized showers and thunderstorms over the Southwest Atlantic. The center is estimated to be located near 27N/71W drifting slowly towards the north-northwest. Estimated winds are near 40 mph with a minimum pressure of 1006 millibars. The center was very difficult to locate because cyclonic turning covers a large area; in fact, those coordinates represent the mid-level center of this puzzling disturbance. Satellite imagery continues to reveal a non-tropical/subtropical structure with much of the deep convection arching north and east of the center due to southwesterly flow around the associated upper trough. Further satellite analysis revealed 90L is merging with the other upper shortwave near the Carolinas and the two should become one over the next day or two. At this point, the system will be located near the Gulf Stream and has a chance to develop into something subtropical. The Tropical Prediction Center (TPC) gives this a moderate chance of transitioning, which I feel is reasonable. Intensity guidances have become a bit more reasonable taking the system to 45 knots over 25C waters and under 15 knots of shear. Since vertical shear is expected to weaken further, the system already has a closed low, and will be near the Gulf Stream; it is my thinking that it may reach this intensity either as a tropical, subtropical or non-tropical feature.


Figure 1. GOES-East water vapor imagery of the Southwest Atlantic and Caribbean Sea taken at 06:15am EDT showing 90L and the area being watched in the Southwest Caribbean.

The system has been enveloped within a weak steering environment so motion over the past 24 hrs was erratic but it appears the system has commence towards the north-northwest at crawling pace. This motion should continue over the next 2-3 days, which should bring it in close proximity to the East Coast. Through days 3, a very large frontal trough over Eastern Canada digs south and breaks down the ridge that is steering 90L northwestward. The trough eventually induces an easterly movement as it becomes absorbed through days 5. The track guidances have indicated that this will not be smooth with an abrupt change in direction from northwest to east. The nature and timing of this trough will determine how close 90L gets to the coast. It would also determine how far south it might get. Motions associated with these types of system are erratic and very difficult to predict.

The pressure gradient between 90L and high pressure to the north is already producing a large area of gale force winds east of 90L, which is generating 8-14 ft seas as indicated by buoy reports. These and heavy rains should impact the island of Bermuda later today with swells of 15 ft reaching the Southeast coast, particularly the Carolinas, by Tuesday and Wednesday. Expect chances of rain, rough surf and breezy conditions with the threat of rip currents increasing through mid-week.


Figure 2. Bermuda Weather Service (BWS) Doppler radar image taken 06:53am EDT showing the rain shield south of Bermuda.


Figure 3. Southeast United States swell chart in feet valid for the next 48 hrs at 9:00pm EDT, 24 May 2010.

Models continue to indicate that an area of low pressure may develop across the Caribbean Sea later this week. While they have not been consistent with this scenario, conditions may become conducive for development (high SSTs, low shear and the upward pulse of the MJO), so the area will be monitored.

Weather456

90L a little better organize; Hurricane Preparedness Week

By: Weather456, 11:16 AM GMT on May 23, 2010

I continue to follow the progress of Non-Tropical Invest 90L which is located near 24.5N/69.9W with a stationary movement. Estimated surface winds have increased to 30 knots and the pressure is estimated to be near 1006 millibars. Satellite imagery along with surface observations indicated that the circulation has gotten deeper and better organize and can be clearly seen on infrared channels. An ASCAT pass from last night revealed a large area of 30 knot winds on the northeast side of the low level center where the pressure gradient is tightest between 90L and the subtropical ridge. Convection has begun to develop along the edge of the low but is still struggling with 30 knot upper level winds and dry air intrusion. The system is trapped within the associated upper low and thus motion is very slow, keeping the system over 25C waters and providing modest shear. I expect 90L to continue to slowly organize and deepen over the next 24 hrs. Much of the models deepen 90L has it moves slowly towards the north or northwest which would significantly increase the winds. The GFDL and HWRF seem to indicate that 90L will reach winds of hurricane strength and while I do believe these are a little overdone, it maybe gradient-induced winds, that is, winds generated due to the pressure gradient between 90L and the subtropical ridge. The sea surface temperatures and ocean heat content is very low in the area and thus the processes of deepening will likely be baroclinic in nature which presents the idea of 90L remaining non-tropical. As the system nears the Gulf Stream, SSTs become much warmer and might allow 90L to become subtropical before being absorbed late this week. There is a high chance of seeing a gale greater than 50 mph but I will continue to give 90L a moderate chance of becoming a subtropical named storm.



Figure 1. AMSR 85 GHZ imagery of 90L taken around 2:00am EDT this morning revealing a somewhat better organized structure (left) and GOES 13 infrared image taken 6:45am EDT showing continued organization (right).

90L is located within a very weak steering environment, being embedded within a broad upper trough and consequently, the system is barely moving. However, as the upper level low continues to seclude over 90L, high pressure over the Atlantic should allow 90L to move more towards north to northwest over the next 4 days then probably stalled offshore the eastern United States before shifting back northeast under the influence of an advancing trough. Most of the models agree that 90L will become absorbed by weekend. The timing of this trough will determine how close 90L gets to the southeast United States. During this time, the pressure gradient between the system and high pressure to the north will generate gale force winds, producing seas as high as 18 ft. These impacts are expected to reach the island of Bermuda by Monday and the Southeast coast by mid-week. Rough surf may increase the threat of rip currents and cause minor beach erosion and coastal flooding. The areas of highest risk appear to be Bermuda and the Carolinas.

Models continue to foresee the development of a system in the Western Caribbean later this week and because conditions may become a bit more conducive for development, the area will be monitored.


Figure 2. 00Z GFS MSLP forecast for the next 24, 48, 72, and 96 hrs with the arrows indicating the strongest winds and highest surf and dashed lines indicating troughs. Notice that 90L moves towards the northwest towards the southeast coast before becoming absorbed by day 4.


Figure 3. Gale low impacts from sea, wind and rain, where yellow is a low possibility, purple/pink, a moderate possibility and red, a high possibility; based on subjective and objective analysis.

Hurricane Preparedness Week

This week is recognized throughout the hurricane community as hurricane preparedness week with today's theme, understanding hurricane history. In recognition of this, I created a video montage of some notable past storms. Throughout the week I will present hurricane tips on hazards, forecasting and planning to bring awareness on the importance of hurricane preparedness. The 2010 Atlantic hurricane season is expected to be well above average and this should be more than enough reason why you should take this week to formulate a disaster plan.



Weather456

Non-Tropical Invest 90L

By: Weather456, 10:31 AM GMT on May 22, 2010

Non-Tropical Invest 90L is estimated to be located near 26N-69W with an estimated central pressure of about 1011 millibars. The system is moving slowly off towards the west with maximum possible winds near 30 mph. Satellite imagery showed a very broad and ill-define center of low pressure which was difficult to locate. The center was relocated about 3-4 times over the past 24 hrs as you would expect with such weak systems. Shortwave infrared imagery was used to locate the center and revealed much of the convection remains on the eastern flank with dry air intrusion covering the center and western flank due to the mixing of 30-40 knot upper winds. Further satellite analysis showed the system is associated with a shortwave aloft which is amplifying. Expect an upper level circulation to develop above the surface low over the next few days which is the beginning stages of subtropical development.


Figure 1. NASA GOES infrared image of nontropical invest 90L.

Development will be slow to occur since the system is currently located in a high shear environment, mid-level dry air and sea surface temperatures around 23-26C. Vertical wind shear is expected to remain moderately unfavourable over the next 3 days but as the associated upper shortwave aloft secludes, vertical shear should relax to about 10-15 knots, allowing any transition to take place. Most of the global models have responded by foreseeing a storm of moderate subtropical/tropical storm strength with the ECMWF, the most aggressive, with a strong subtropical/tropical storm or weak hurricane. It is unlikely that we will see a hurricane from 90L due to the heat content in the Southwest Atlantic. However, there is a moderate to high chance of seeing a storm greater than 50 mph, whether tropical or non-tropical. This is not reflected by the latest statistical intensity guidances which at this point are rather useless.

Currently the system is drifting west under deep layer ridging over the Atlantic and this motion should continue over the next 24 hrs. Blocking high pressure over the Atlantic and a shortwave over the CONUS will not allow too much easterly biased to the track guidance with northwesterly motion expected over the next 4 days. The global models appear to have the best consensus and guidance thus far, taking the system northwestward towards the Southeast by Wednesday. This guidance is very feasible and this is the guidance I am going with.


Figure 2. Synoptic overview of the Western Atlantic showing the upper wind flow (white arrows), surface-upper lows, surface-mid level anticyclones (blue) and shortwave troughs.

Due to the pressure gradient between the low and the high that is steering it, strong winds will developed on the eastern and northern side of the system, generating swells as high as 18 ft. Much of this will impact Bermuda with high surf by Monday and reach the Southeast by mid-week. Expect high surf with the threat of rip currents, minor beach erosion and coastal flooding, especially along the Carolinas.


Figure 3. Gale low impacts from sea, wind and rain, where yellow is a low possibility, purple/pink, a moderate possibility and red, a high possibility; based on subjective and objective analysis.

The other area of concern lies in the southwest Caribbean where most models continue to foresee the development of a weak system late next week. Any system here will be monitored closely since the shear forecasts are now indicating a more favorable environment as the sub-equatorial ridge and jet stream pulls north. What is interesting is that, initially the system would have struggle if the time frame of development was mid-next week. But because the time frame keeps increasing (now late next week), the possibilities of development are increasing since it gives more time for the subtropical jet stream to shift north. Currently, just a few scattered showers are in the Western Caribbean but the area will be monitored during the course of next week.

Weather456

Low pressure system develops east of the Bahamas; No change to Caribbean potential

By: Weather456, 9:38 AM GMT on May 21, 2010


Figure 1. Synoptic overview of the Western Atlantic this morning showing the two shortwaves over the CONUS and Atlantic in relation to the surface lows.

Satellite imagery and surface observations indicated that an area of low pressure has developed just east of the northern Bahamian Islands centered on a 1012 mb low near 26N-74W, moving slowly eastward. Satellite imageries show the center is devoid of any convection, with much of it on the east side due to fast upper winds. This is typical for most hybrid lows as upper forcing is one of their sources of energy. I cannot tell if the low is closed since I have no surface observations indicating west winds. However, a partial ASCAT and shortwave infrared images lead me to think that the low is almost closed.

A series of shortwave troughs along the Eastern Seaboard and over the Central CONUS are the main initiators of this low pressure area. The first is expected to lift out by Saturday, with ridging taking over, leaving the low pressure to meander between Bermuda and the Bahamas. The second shortwave move north of the area in about 3 days but because of blocking high pressure over the Atlantic, the southern portion secludes and interacts with the surface low. Initially, the system is vertically tilted but through day 5, the surface low moves under the secluded low aloft and transition to subtropical begins. During this time, the system drifts back north-west under the influence of the high to the north.


Figure 2. GFS surface pressure and rainfall analysis valid 25 May 2010 showing the blocking high, moisture fetch, tropical influx and forecast track.

Most of the models agree that the system will become vertically stacked within an environment favourable for subtropical transition. First, the low is blocked off from any cold air supply to the north by the bridging high and has a steady flow of tropical moisture from the south thus increasing the chance for it to become warm-core. Second, the system forms at the split of the subtropical and polar jet streams where shear is low and third, sea surface temperatures are above the 23C needed for subtropical cyclogenesis and near 26-28C near the Gulf Stream. The GFS is the only model which weakens the low offshore the Southeast United States for no apparent reason. Given these parameters, I continue to give a moderate chance of us seeing Subtropical Storm Alex next week.

The forecast track of this hybrid low is pretty simple. The initial low near the Bahamas will move north-eastward under the influence of the first shortwave over the next 2 days but as the trough lifts out and high pressure builds north of the area, the system is forced back towards the northwest. I suspect the system will get as far east as 65W before turning back. Through days 3-5, the system steadily moves northwestward towards the coast of the United States, probably brushing the Carolinas. Some models have the system going southwest, making an entire loop, before being picked up by a trough through days 7.

Due to the pressure gradient between the low and high, the system will be generating pretty strong winds, as high as 55 mph, with seas of 12ft by Sunday which will impact Bermuda with high surf. The strongest winds remain offshore and the island only experiences 30-35 mph. By Monday, swells increase to 16 ft, reaching the US coast by Tuesday. I expect some level of beach erosion and the risk of rip currents along the Carolinas, Georgia and Florida coasts. Any rain from the system would occur though Wednesday as the system nears, possibly with a moisture fetch to its north.


Figure 3. Gale low impacts from sea, wind and rain, where yellow is a low possibility, purple/pink, a moderate possibility and red, a high possibility; based on subjective and objective analysis.

Most of the models continue to forecast a weak depression or storm in the Caribbean late next week. It seems as though, everytime I conduct an update, it’s always within the 5-7 day time frame which questions the consistency of the models with this system. Nevertheless I will continue to monitor the Caribbean for development since thunderstorms are already developing over the area. Any system here will likely affect Cuba, Jamaica or Hispaniola with heavy rains. None of the reliable models show the system reaching moderate tropical storm strength due to the presence of vertical shear.

Weather456

Gale force system expected this weekend; Potential system in SW Caribbean

By: Weather456, 11:06 AM GMT on May 20, 2010


Figure 1. Very complex weather pattern set-up across Southwest Atlantic with a shortwave (purple) and its associated frontal boundary (blue) along the Eastern CONUS. A second shortwave and low over the Central CONUS. The yellow arrows represent the upper air flow and the green arrows represent the flow of warm tropical air. All ingredients of a potential gale and/or subtropical system.


We have a very complex weather pattern that will serve as the precursor of a possible subtropical depression as early as this weekend over the Southwest Atlantic. First we have a shortwave and its associated frontal boundary draped along the Eastern seaboard. Second, we have a broad area of low pressure sitting near the Bahamas, either in the form of a surface trough or actual low level center. Third, we have a plume of tropical moisture extending from the Northwestern Caribbean into the Southwest Caribbean. Models have been indicating with good consensus, that the shortwave will begin to initiate an area of low pressure near the Bahamas as it interacts with the southern portion a dying front in two days. Meanwhile, the base of shortwave splits leaving additional energy behind to continue genesis of a gale center by day 3. By day 4, the gale center interacts with a second shortwave and becomes vertically stacked through days 5-6. At this point is where the system may transition to Subtropical Storm Alex.

The system in the early stages forms under high vertical shear in a baroclinic zone with dry air entrainment; but as the subtropical and polar jet streams split, vertical shear weakens. This does not occur until day 4, so this is when I expect any transition to occur. The system is also under waters well above the 23C requirement for subtropical storm development and border the 26C isotherm needed for tropical cyclones. If the system manages to enter the Gulf Stream as indicated by some models, it may fully transition. Atmospheric pressures at buoy 41046 just east of the Bahamas continue to fall which is a good indicator that a low pressure area is present. There is also a supply of warm tropical air into the system which increases the likelihood of transition.

Anything forming here will be under the influence of bridging high pressure to the north and will likely retrograde back west. Both the ECMWF and GFS show this becoming a significant system off the coast of the Southeast United States in 6 days.

Based on this data, the models seem to be verifying and thus given the current situation I raise my chances of a gale center to high but continue to give a low-moderate chance of becoming subtropical or tropical.

Regardless of development, heavy scattered showers and thunderstorms will continue over the Caymans, Jamaica, Cuba and the Bahamas; today, Friday and Saturday as genesis occurs.

Seas of 14-18 ft and gale force winds are expected to impact Bermuda by Sunday through Tuesday and beyond then, these conditions may reach the Carolinas and the Southeastern United States.

The second system that we maybe tracking next week, forms in the Southwest Caribbean Sea from a broad area of low pressure. Models continue to indicate that a series of tropical waves will energize a broad area of low pressure over the Caribbean in about 3 days. Most of the models agree that some level of development may take place in the extreme southwest Caribbean, where pressures are low, ssts and moisture are high and vertical shear is low. The models agree the system will move between north and northeast without deepening much through 5-7 days due to the presence of vertical shear. I expect that a broad area of low pressure will develop over the area by Sunday but there is only a low-moderate chance of a depression forming. If it does form, it will likely remain a weak system as it heads north-northeast, bringing heavy rains to Hispaniola later next week.

It appears the SW Atlantic disturbance will be deeper than the SW Caribbean disturbance but the latter is the more dangerous of the two. Irony.


Figure 2. GFS forecasted MSLP and accumulated surface precipitation for Wednesday 26 May 2010.

Weather456

40-50% chance of La Nina this summer/fall; two areas to watch next week

By: Weather456, 9:47 AM GMT on May 19, 2010

El Nino Transition to La Nina


Recent observations by the Climate Prediction Center (CPC) and Australia’s Bureau of Meteorology (BOM) have indicated that El Nino conditions have weakened across the equatorial Pacific and transition to neutral is underway. They have also pointed out that further cooling of the sea sub-surface might result in the development of a La Nina over the next 3-6 months which would be considered a rapid transition phase and there have only been a handful since records began. Today we are going to assess the likelihood of such transitions stressing on the oceanic aspect of the El Nino Southern Oscillation (ENSO).

El Nino Transition Years

There have been 17 El Nino events since 1950 based on NOAA’s Oceanic Niño Index (ONI) which defines an El Nino (La Nina) as a positive (negative) seasonal ONI greater (less) than 0.5. Of these 17 events, 7 transitioned to La Nina and of which 5 were considered rapid transitions. This implies that roughly 30% of El Nino events results in a transition to La Nina and 70% of transitions were rapid.


Table 1. Showing the 7 El Nino years that transition to La Nina and the nature of the transition.

Mechanisms behind transition

The Thermocline


Figure 2. Animation of the sea level anomaly/sea surface temperature anomaly above and the thermocline (depth of 20C waters) below. The first few frames represent a neutral state. During the onset of El Nino, the thermocline becomes shallower in the west and deeper in the east. During the height of El Nino, the thermocline is the same depth everywhere. During the decay of El Nino and onset of La Nina, the thermocline deepens in the West and becomes shallower in the east thus providing more cold water for upwelling. Animation credit: Joseph Barsugli, NOAA, ESRL.

The thermocline is a thin but distinct layer in the ocean, in which temperature changes more rapidly with depth than it does in the layers above or below. The thermocline in the equatorial Pacific Ocean is normally found between the 15-20C isotherm; is a main indicator of the current ENSO mode and can be use to forecast the transition of the oscillation. The thermocline is naturally deeper in the Western Pacific and shallower in the Eastern Pacific due downwelling of warm waters and upwelling of cold waters, respectively. A shallower thermocline provides a greater supply of cold waters for upwelling, while a deeper thermocline provides a lesser supply of cold waters for upwelling.

During El Nino events, Kelvin waves propagate westward and weaken the easterly trades thus causing warm waters to advect from west to east. Thus, the thermocline becomes shallower in the Western Pacific and deeper in the Central and Eastern Pacific.

During an El Nino to La Nina event, the thermocline levels off as the west becomes shallower and the east becomes deeper. Eventually the thermocline is levelled and shallow throughout the entire equatorial Pacific. Any weak fluctuation in surface winds causes the sea surface to cool and promotes upwelling. This may set the stage for La Nina to develop and the transition may only take a month or two.

As the Kelvin waves continues west, it hits the equatorial coast of South America and propagates back towards the west, inducing upwelling over the Eastern and Central Pacific and lowering the depth of the thermocline there. Consequently, the thermocline becomes shallow in the Central/Eastern Pacific. Historical data shows lower anomalies first develop in the Central Pacific and propagate towards the east. In fact, all of the years that had a gradual or rapid transition first developed lower anomalies in the Central Pacific, which eventually propagated towards the Eastern Pacific. In 2010, the same observations were noted during April, where the 20C isotherm was anomalously low in the Central Pacific. Should any wind fluctuation arise, upwelling will intensify across the Pacific and these lower heights will eventually head east, inducing a La Nina.


Figure 3. BMRC ocean analysis of 20C isotherm anomaly (m) with temporal change on the y axis and spatial scale on the x axis. From this image we see the shallower thermocline begins in the Central Pacific and propagates to the Eastern Pacific.


Figure 4. BMRC analysis of the monthly mean 20C isotherm anomalous depth (m) for the April of the selected years. A shallower thermocline provides a greater supply of cold water for upwelling and this was the case of all transition years and April 2010. Any increases in tradewind will likely upwell this cold water.

Sea Surface Temperatures

The appearance of cooler waters in the Central Pacific indicates the decay of El Nino. Further cooling increases the temperature gradient between the Central/Eastern Pacific and the Western Pacific which increases the easterlies and promotes further upwelling. Once this process becomes self sustaining, then La Nina develops. Now the rate and nature of this warming indicates the likelihood of La Nina by the peak of summer.



Figure 5. NOAA’s Oceanic Index (OI) analysis of sea surface temperature anomalies for January, April and August of the selected years. Notice the distinct patterns and distribution of warm and cold anomalies as El Nino (January) transitioned to La Nina (August). Both 1998 and 2010 had basically the same rate of cooling this far.

Transitions based on sea surface temperature anomalies can be summarized into two categories – cool anomalies that develop in the eastern Pacific then propagate towards the central Pacific – 1988, 1995, and 2007, while the other half is cool anomalies that develop first in the central Pacific and stretch towards the eastern Pacific – 1985 and 1998. Basically cool anomalies begin to develop in both categories by April except for 1998 and 2010. This implies that El Nino is weakening at the same rate in both years, another reason why 1998 is a good analogy to 2010.

The hurricane season started late in 1998 with Tropical Storm Alex developing on July 27 and this could imply a late start to 2010. However, as of 17 May 2010, cool anomalies have already developed in the Central Pacific and this was not the case on 16 May 1998. This implies that even though January-April rate of cooling was the same for both years, results from May of each year revealed 2010 is cooling much faster than 1998. This could trigger the onset of La Nina much quicker than 1998 and in line with other years.


Figure 6. NOAA/NESDIS SST anomalies on May 16 1998 (left) and May 17 2010 (right) showing the distinct difference in temperature anomalies in the Central Pacific.

Sub-Surface Temperatures

The upper ocean heat content is another way of measuring the onset of La Nina. During the period January to April 2010, the average temperature of the upper 300 meters of the equatorial Pacific between 180W and 100W (Central Pacific) cooled by 1.2C, which the highest of the selected years. Rapid transitions to La Nina occurred when this portion of the sub-surface cooled by about 1C over a four month period. In 2007, much of the cooling took place between the four month period starting November 2006 and by April; the cooling had slowed on its way to La Nina.


Table 2. Showing the 7 transitioning El Nino events, the nature of the transition and the change in sub-surface temperatures from January to April.

The Southern Oscillation Index

Sustained positive values of the Southern Oscillation Index (SOI) implies greater pressures over the south-central Pacific and lower pressures over Australia, thus increasing the speed of the trades (particularly the southeast trades) which causes upwelling in the Central Pacific and the onset of La Nina. The opposite occurs during the onset of El Nino.

In the case of rapid transition to La Nina, 3 of the 5 years had an increase greater than 20 over the 6 month period December (the previous year) to May (the current year). During the previous 5 months, the values of the SOI have increase by almost 26, the largest of any transitioning year, with 1964 and 1998 close behind. It is unclear why 2006-2007 had only an increase of 4.3. As we mentioned before, these sustained values could mean the onset of La Nina. However, sometimes the MJO can have influences on the SOI index by creating lower pressures over Australia and Indonesia that otherwise would not have been there thus increasing the SOI. In order to assess whether this was ENSO or MJO related we would have to continue to monitor the SOI over the upcoming months as the MJO moves away from the area.


Table 3. Showing the 7 transitioning El Nino events, the nature of the transition, the change in sub-surface temperatures from January to April and the greatest SOI change over the 6 month period from December to May.

Numerical and Climate Models

The majority of dynamical and statistical model forecasts for sea surface temperature anomaly for April showed that anomalies cooler than -0.5 are expected by August, September and October (ASO). But which model is more valid? From personal experience and evidence, the Japan Meteorological Agency’s FRCGC model and the European ECMWF are the highest verifying models during transition of El Nino to La Nina, which I suspect is a bit more challenging for models than just predicting onsets. For example, in April 2007, the European model predicted -0.5 anomalies by July and -0.4 was actually measured. The Japanese model predicted -0.8 anomalies by August and -0.7 was actually reported.

Currently, the ECMWF is predicting cool anomalies of -0.7 by July and the JMA is predicting cool anomalies of -0.6 by August. It is likely that the oceanic part of ENSO will border the La Nina range by August of 2010. Further cooling is expected by year’s end.


Figure 7. Model forecasts of ENSO issued April 2009 based on March conditions.

Summary

We have seen that that roughly 30% of El Nino events results in a transition to La Nina and 70% of transitions were rapid. By comparing this year’s conditions with that of previous transitions, we can assess the likelihood of a La Nina transition, either gradual or rapid. Based on the depth of the thermocline, there is a great supply of cool waters for upwelling. Increases in the SOI will bring increase in trade winds which will upwell this water, resulting in a cooling of the sea surface and sub-surface. There is evidence that this is already occurring and based on historical transition events, there is a 40-50% chance that La Nina will develop this summer in the waters across the equatorial Pacific. Whether the conditions lag or not will be determined by the atmospheric variables such as tradewind index and SOI. The transition to La Nina implies increase hurricane activity in the Atlantic this year.

Other Blogs and Resources

The Southern Oscillation Index
The Earth’s Angular Momentum (Earth’s Rotation) and ENSO are linked
El Nino and the Thermocline
El Nino Southern Oscillation – Climate Prediction Center
Bureau of Meteorology Research Centre (BMRC)
The International Research Institute of Climate and Society (IRI) ENSO Update and Forecast

Tropical Update

Based on the current satellite images, large scale upward motion is moving into the Western Atlantic. We continue to have this mess of convection over the Northwest Caribbean associated with a surface trough enhanced by upper level divergence in the subtropical jet. Expect this activity to spread north-eastward over Cuba, the southern tip of Florida and the Bahamas over the next day and two.

We have a very active tropical wave along the ITCZ over the Central Atlantic that may have tried to organize a bit but is located too far south to do so effectively. Intense clusters within each side of the wave axis. Expect to reach the south Caribbean by Saturday.

We may have two tropical disturbances to watch later next week as global models have continue to increase their consensus about the development of a hybrid system east of the Bahamas and a tropical cyclone in the Southwest Caribbean.

The first solution dictates that a shortwave begins to dig across the Western Atlantic through the next 3-7 days inducing a surface trough of low pressure east of the Bahamas in the process. As the trough continues to amplify it splits beyond 7 days. Enveloped in this trough is a hybrid type system trapped in the subtropics by bridging high pressures. The GFS develops the cyclone and take it out to see as a non tropical system but some of the energy stays behind. The CMC foresees a stronger cyclone that retrogrades back west a shallow non-frontal warm-core system. The ECMWF has the most aggressive solution and like the CMC retrogrades the system back west once it forms nears the Bahamas. These are feasible solutions but it is likely anything forming here will be subtropical at best based the vertical shear gradient north of the subtropical jet stream, sea surface temperatures of 24-26C and type of genesis.

This feature is mostly a threat to Bermuda and possibly the southeast United States later next week. It may serve to bring heavy rains, high winds and rough surf across the Southwest Atlantic, regardless of development.

The other system that the models are developing is a tropical depression or storm in the Southwest Caribbean. Genesis originates during the passage of a tropical wave over Venezuela that you guys know I have been tracking since last weekend. The wave initiates a broad low pressure just north of Panama in about 3-4 days. Initially the system is slow to move because it is locked in weak steering flow due to the genesis of the hybrid low to its north. Through days 5-6 the storm slowly drifts north as the trough associated with the hybrid system to the north continues to dig deeper. Through day 7, the trough should have sufficient influence on the system to pull it gradually towards the northeast. Now the ECMWF, NOGAPS, GFS and CMC all show this solution. The environment in the Southwest Caribbean will be conducive as shear forecasts are becoming a bit clearer. The MJO pulse is expected around this time, pressures are below normal over the area and sea surface temperatures are around 28C. However, the models are also in consensus that the system will struggle later in the cycle as it moves north into a higher shear environment.

Most of the models show the system eventually affecting Hispaniola with heavy rains.

I’m highly confident that a low pressure system will form east of the Bahamas, but gives it a low-moderate chance of becoming subtropical. I’m highly confident that a broad area of low pressure will develop in the Southwest Caribbean and gives this area a moderate chance of being designated an invest.

I will continue to monitor for any changes.


Figure 8. Next week's tropical and model summary.

Weather456

Warmest April on Record

By: Weather456, 10:39 AM GMT on May 18, 2010

Warmest April on Record

The National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center (NCDC) issued their monthly global analysis yesterday reporting that April 2010 was the warmest April on record. The combined global land and ocean average surface temperature for April 2010 was the warmest on record at 14.5°C (58.1°F), which is 0.76°C (1.37°F) above the 20th century average of 13.7°C (56.7°F). This was also the 34th consecutive April with global land and ocean temperatures above the 20th century average, the center reported. Worldwide ocean temperatures were the warmest on record with the warmth most pronounce in the equatorial portions of the major oceans, especially the Atlantic. Land surface temperatures were the third warmest on record.

Worldwide temperature anomalies were reported by the German Meteorological Service (Deutscher Wetterdienst), the Beijing Climate Center (BCC), the India Meteorological Department (IMD), and Australia’s Bureau of Meteorology (BOM).

Warmer than normal temperatures basically covered every corner of the globe except for Northeastern Asia, the Southern Ocean, parts of western North America and the Southeast United States. The latter was likely due to the effects of El Nino and the negative phase of the North Atlantic that I discussed last week.


Figure 1. Temperature anomalies for April 2010 are shown on the dot maps above which provides a spatial representation of anomalies calculated from the Global Historical Climatology Network (GHCN) and sea surface temperature anomaly developed by Smith et al. (2008).

Solar Cycles

It is likely that solar cycles over the recent three decades have minimal impact on climatic warming here on earth. For example, we are currently in the depts of a solar minimum that began around the beginning of the last decade, yet global temperatures continue to rise. The same was true for the mid-late 1990s which accounts for the 2nd warmest April on record – 1998. I have read numerous papers from 1998 to 2009, ranging from Solanki in 2003 to Lockwood in 2008 and the conclusion is that solar forcing has decline over the past 20 years yet surface global temperatures continue to rise. It is likely that other forces here on earth are responsible for the warming of the earth since theoretically, the globe was to cool.


Figure 2. Annual global temperature change (thin light red) with 11 year moving average of temperature (thick dark red). Temperature from NASA GISS. Annual Total Solar Irradiance (thin light blue) with 11 year moving average of TSI (thick dark blue). TSI from 1880 to 1978 from Solanki. TSI from 1979 to 2009 from PMOD. Image credit: SkepticalScience.

El Nino

El Nino is probably one of the major causes of year to year anomalies in global temperatures. While, global temperatures have trended upwards over the past 20 years, El Nino is largely responsible for year to year variations. There is evidence that the April (I choose April for this report) succeeding an El Nino event is often marked by an increase in mean global temperatures. For example, the top 4 warmest April – 1998, 2005, 2007 and 2010 were all preceded by an El Nino event – 1997, 2003-2004, 2006 and 2009.


Figure 3. NASA April mean global temperature from 1990 to 2008 in degrees F showing that 4 of 6 increases in global temperatures occurred in years succeeding an El Nino event. All these four years had active hurricane season the following summer.

Greenhouse Gases

It has become quite apparent that increases in gases that trap the sun’s heat – greenhouse gases - are tied to increases in global temperatures. There are three main greenhouses gases that we use in relation to global warming – nitrogen oxide, carbon dioxide and methane – but for this report, carbon dioxide, which is the most common and effective greenhouse gas of the three, will be used. Carbon dioxide in the atmosphere fluctuates year to year and season to season depending on land and vegetation variations. For example, one of the centers for measuring atmospheric carbon dioxide - Mauna Loa, Hawaii, measured 387.35 parts per million carbon dioxide in 2009 and 379.76 parts per million in 2005. In addition, compare 1999 to 2009, which had 368.14 parts per million and you get an increase of 19 parts per million over a 10 year period. These numbers may be confusing but they indicate, long-term speaking, that carbon dioxide is increasing in the atmosphere and it is tied to warmer global temperatures.


Figure 4. Atmospheric C02 levels during April measured at Mauna Loa Observatory, Hawaii. The upper safety limit for atmospheric CO2 is 350 parts per million (ppm). Atmospheric CO2 levels have stayed higher than 350 ppm since early 1988. Image credit: C02Now.


Figure 5. Green line is carbon dioxide levels from ice cores obtained at Law Dome, East Antarctica (CDIAC). Blue line is carbon dioxide levels measured at Mauna Loa, Hawaii (NOAA). Red line is annual global temperature anomaly (GISS). Image courtesy SkepticalScience.

Tropical Cyclones in the Atlantic

Increases in April temperatures over the past two decades have been tied to increase in hurricane activity over the Atlantic and it’s so that these years coincide with a weakening El Nino. Look at the years presented – 1995, 1998, 2002, 2005, and 2007, with the exception of 2002 which had an El Nino developing by April, all these years had well above average hurricane activity. The years 1998 and 2005, the two other warmest April, are already considered analog years. The NCDC also stated in their report that the warmest anomalies of sea surface temperatures were in the Atlantic. This overwhelming consensus of data is an indication of an above normal hurricane season this year, not just numbers but intense hurricanes.

Summary

It is obvious that with each increasing year, global temperatures are increasing. April 2010 on land and both water was the warmest on record; breaking records set in 1998 and 2005, just 12 and 5 years ago. Probably the largest factor in this increase in temperature is the increase in greenhouse gases, with smaller scale influences by El Nino. It is unlikely that solar cycles have any major impact on earth’s climate over the past decades. The power of knowledge should use to power change because just reporting the facts is only part of the solution; bringing awareness to the globe constitutes the second half. The earth is heating up.

Tropical Update

I continue to follow the weather pattern across the Western Atlantic and nothing significant has occurred. We continue to have deep convection over the Northwestern Caribbean being generated by upper divergence within a diffluent zone of the subtropical jet, aided by surface speed convergence. CIMSS wind analyses indicate that the convection is removed from the line of convergence near the Belize/Yucatan coast which indicated some of this convection is elevated in nature. Expect continued shower and thunderstorm activity over this region throughout today, which includes parts of Central America, the Caymans, Cuba and possible some moisture reaching the Bahamas.

A weakening upper trough remains over the Caribbean still helping to enhance tradewind moisture over Puerto Rico and the Lesser Antilles. The extent of such showers should be less today.

A tropical wave moving into South America, now over Venezuela after bringing scattered shower activity to the southern Lesser Antilles on Sunday and Monday. Expect some lingering isolated showers today with the bulk of the wave energy over the continent. Expect the tropical wave to continue over the South American landmass enhancing shower activity, especially during the afternoon over the next 3 days. It reaches the southwest Caribbean in about 4 days.

Models continue to agree that a broad area of low pressure will develop over the Southwest Caribbean later this weekend into next week as the tropical wave passes. The GFS and ECMWF, two reliable models show development of this wave by next week as it remains in a relatively favourable environment in the extreme southwest Caribbean. I am confident that a broad area of low pressure will develop but less confident that it will develop due the small breathing space it has since vertical shear gradient is very steep to the north (increases rapidly as one heads north). It’s too early too tell whether it will develop or where it will go but models are indicating in the long-run that it may head for the northern Caribbean as a weak system. Regardless of development, areas like Colombia, Panama, Costa Rico and adjacent waters can expect an increase in shower and thunderstorm activity this weekend into next week.

Models are also indicating that a trough-split scenario may give rise to a non-tropical feature east of the Bahamas basically around the same time frame. The system eventually becomes trapped by a blocking high and retrograde back west over 23-25C waters, which can support hybrid systems. Models are less enthusiastic on this feature than they were yesterday but still indicate a possibility that a hybrid system may form. The system forms at the split of the subtropical and polar jet streams which is ideal for May type systems of this nature. Regardless of development, Bermuda may be visited by gusty winds, choppy seas and heavy rains later next week.

I will have more updates on these features as time goes on.


Figure 6. Water vapor depiction of several features over the Atlantic, Caribbean Sea and Gulf of Mexico this morning.

My next blog will discuss this year’s possible transition to La Nina.

Weather456

The Caribbean's Strive for Renewable Energy; Tropical Update

By: Weather456, 1:02 PM GMT on May 17, 2010

The Western Atlantic remains convectively active this morning. This activity is being caused by instability associated with a weak short-wave that extends from a mid-latitude storm over CONUS to the Isthmus of Tehuantepec aided by low level speed convergence. Maximum convergence and divergence coincides with the deepest convection near the Yucatan Peninsula. Here, further lifting will likely lead to the development of a surface trough. No development of this surface trough expected but heavy showers will continue across the area as the trough pulls slowly west; including, western Cuba, parts of Central America, the Caymans and Yucatan Peninsula.

Upper trough remains stationed over the Caribbean providing dry, stable air near its axis and largely diffluent flow on the eastern flank. The upper trough is expected to lift and be replaced by upper ridging over the next 24-48 hrs. Until then, upper diffluence will continue to enhance tradewind moisture over the northeastern Caribbean. Expect continued isolated showers over the Leeward Islands and Puerto Rico.

Slow moving tropical wave near 56-57W will near the islands later today and this evening bringing isolated thunderstorm and shower activity.

Most of the models agree that this wave will help to enhance a broad area of low pressure (or vice versa) across the Southwest Caribbean later this week. The CMC thinks development will take place in the Eastern Pacific, while the GFS, NOGAPS and ECMWF has a weak tropical disturbance originating from this area of low pressure. I’m confident that a broad area of low pressure will develop over the area later this week into weekend but gives it a low chance of significant development due to unfavourable upper winds just to its north. If the system is able to linger long enough over warm sea surface temperatures and for the ridge to sufficiently build, then the chances increases but for now based on what I’m seeing, I’m not expecting much. Heavy rains however will spread over Colombia, Panama and Costa Rico as the broad area of low pressure develops. I will continue to monitor for any changes.


Figure 1. Water vapor imagery of the Western Atlantic this morning depicting several synoptic features. The area around the SW Caribbean is a forecast valid through 4-5 days.

The Caribbean’s Strive for Renewable Energy: Why Strive for Greener Energy

The islands of the Caribbean are net energy importers, with the exception of Trinidad and Tobago. Countries across the Caribbean get most of their energy through the import of oil and countries like Aruba, Curacao, and the U.S. Virgin Islands, are important centers for oil refining and storage, due to their proximity to the U.S. market. In recent years, there has been concern that higher global oil prices will impair the Caribbean economies, as they are highly dependent upon oil for their energy needs. In response, the island nations have been discussing ways to promote alternative energy sources and better integrate their energy sectors.

The Caribbean Renewable Energy Forum was launched in October 2009 with its main mission is to address how Caribbean countries can best exploit their sources of Solar, Geothermal, Wind, and Hydro energies and becomes less dependent on energies from North America, South America and the Middle East. Their next meeting will be held in the Bahamas on the 14th and 15th of October this year and is a venue I hope to attend due my country dependency on foreign oil.

The Caribbean is a hot spot for alternative forms of energy and today we are going to look at what makes the Caribbean such a prime place for renewable energy and why we should integrate these forms into our economies.

Reasons Why the Caribbean Should Strive For Greener Energy

Global Warming and Climate Change

Nowhere in the Western Hemisphere will suffer more from climate change than the Caribbean region. Over the past decade, the Caribbean has suffered from a barrage of intense tropical cyclones that have killed thousands and crippled fragile economies. Last July, I presented an excellent article on the effects that climate change and rising ocean temperatures have on Caribbean coral reefs. Record high ocean temperatures in 2005 devastated half the coral reefs in the Caribbean and this year, it’s even hotter. The melting of glaciers also poses a threat to small Caribbean islands due to rising ocean levels. There is evidence that increasing C02 emissions from the larger industrialised countries will only form the cause of increasing global temperatures. Because the Caribbean are heavy oil importers we form a market for these oil giants and by reducing our consumption of non-renewable energy sources we can help do our part in lowering C02 emissions.


Figure 2. Green line is carbon dioxide levels from ice cores obtained at Law Dome, East Antarctica (CDIAC). Blue line is carbon dioxide levels measured at Mauna Loa, Hawaii (NOAA). Red line is annual global temperature anomaly (GISS). Image courtesy skepticalscience.com

Fragile Economies

Most Caribbean economies are small and heavily dependent on foreign oil imports which present a valid reason why the Caribbean should continue to switch to alternative ways of generating energy. The economies are also considered developing so the hassle of integrating alternative sources of energy should be low as oppose to developed and under-developed countries. Fluctuating oil prices have the power to cripple Caribbean economies that have become heavy oil importers, by increasing energy bills and reducing consumer expenditure in other sectors of the economy. Furthermore, oil and coal reserves will likely last to the end of this century with each and every passing decade, the law of supply and demand will only cause further increases in oil prices.


Figure 3. Net exports of petroleum for four Caribbean countries with negative values showing more imports than exports. Source: US Energy Information Administration (EIA).

Environmental Risk

Air quality in the Caribbean is relatively good compared to larger industrialisation. The large amounts of aerosol over the Caribbean are mostly in the form of dust blown from Africa which is a natural form of nature. However, there are a number of other air pollutants and their concentrations can measure how clean the air is, that is, air quality. One of these pollutants that is often use to measure air quality is nitrogen dioxide which is a reddish-brown toxic gas that has a characteristic sharp, biting odour and is an immediate result of industrialisation of nitric acid. Nitrogen dioxide is choking and poisonous. Furthermore it forms the catalyst on which sulphuric acid or acid rain forms.

High levels of nitrogen dioxide are found in the highest industrialised areas of the Caribbean – Hispaniola, Cuba, Venezuela, Colombia and Mexico. Smaller amounts were found near Trinidad and Tobago. Even larger amounts where found across the heavy industrialised areas of North America. This poses a concern for Caribbean nations as high levels of acidity in rainfall will be harmful to life on land and in the water usually far away from the source of emission.

Another important environmental risk is that high levels of carbon dioxide absorbed into the ocean leads to marine acidification which is detrimental to coral reefs. Recent observations have shown that oceanic pH levels continue to increase as atmospheric carbon dioxide does. Coral reefs form a vital part of the service and agricultural sector of most Caribbean countries and the loss of such would hamper Caribbean economies.

The Caribbean, as we have found out, is a leading market when it comes to oil and other forms of non-renewable energy, thus reducing this market should be of most priority and the only way to do so is to reduce our dependency on foreign oil and gas.



Figure 4. Nitrogen dioxide concentrations for 2009 (top) and May 15 2010 (bottom) in molecules per cm2. Notice heavy nitrogen dioxide concentrations coincide with the heavy industrialised areas of North America. Also notice that nitrogen dioxide plumes over the Central Caribbean south of Hispaniola, illustrating the transport of such pollutants from source of emission. Image credit: NOAA's Office of Satellite Data Processing and Distribution (OSDPD).

Weather and Climate

The Caribbean region lies within the deep tropics and thus receives huge amounts of solar insolation from the sun. Solar power is created by capturing sunlight energy and converting that to electricity. Solar panels in various forms can take advantage of the intense tropical sunshine received by the islands of the Caribbean. Rooftop solar panels may be a cost-effective means to power homes, offices, hotels, resorts and other structures in the Caribbean, particularly due to the region's strong and abundant sunshine. Solar cells also can be used for water heating and supplying electricity to certain appliances and infrastructure.

Solar energy cannot compete with other forms of energy as yet but is getting recognition due rising cost of oil and intense sunshine. Solar systems have the advantage of low maintenance (only cleaning) and can also save some cost by replacing traditional roofing systems.


Figure 5. Solar insolation during the 1 month period between April 1 and April 30 in watts per square meter. By looking at this map we can see how much solar energy the earth receives during April. The Caribbean lies within the deep tropics and so receive about 500 watts per square meter and when you do the math of all the islands that have sunny days most of the year, the yearly figures can support atleast 30% of current electricity consumption per year. Image credit: NASA Earth Observations (NEO).

Wind power is created by capturing the energy within wind and converting that into electricity. In some areas, large scale wind farms, either onshore or offshore, are needed to produce an adequate supply of energy to the electric grid. However, in other instances, much smaller scale wind turbine operations may be used for more isolated areas. Although many Caribbean islands have a steady supply of wind from the trades, the visual and environmental effects as well as the high cost of constructing many wind turbines must be considered. Small-scale wind energy production may be the best course for the Caribbean.


Figure 6. NCEP/NCAR scalar wind speed composite mean with prevailing winds overlaid from January to December from 1980 to 2009 which shows the Caribbean, particularly the Eastern Caribbean receives on average about 8-10 m/s winds, which is above the 6 m/s wind require for wind turbines. Some hurricane winds maybe incorporated in this composite but the January to June average is basically the same.

Geology and Geography

The Caribbean is a geologically active area and thus we can really utilise geothermal and hydroelectric power sources.

Hydro power is created by capturing the energy found within flowing water, such as in streams and rivers, and converting that energy into electricity. Examples of hydroelectric power-generation facilities are dams on rivers, which cause the water in the river to flow through the dam, spinning turbines and creating electricity. Hydroelectric power may be an option on some Caribbean islands, particularly the larger and more mountainous areas, but is not an option for all due to the scale and cost. Also, the effects of a hydroelectric facility on the local landscape and ecosystem are important factors for consideration.


Figure 7. The Coco or Segovia River in northern Nicaragua, one of the largest rivers in Central America, that under good ecological management can be utilized for hydroelectric power. Image credit: Bill Anderson.

Geothermal power is created by capturing energy from heat stored beneath the surface of the earth. Traditionally, geothermal power facilities have been most effective along and near geologically active tectonic plate boundaries. A number of Caribbean islands are along the tectonic plate boundary between the Caribbean Plate, North American Plate, and South American Plate. This position accounts for the volcanic and seismic activity on and near many Caribbean islands. In particular, the Lesser Antilles, including the Windward and Leeward Islands, show potential for harnessing geothermal energy but the difficulty lies in the costs and environmental effects of drilling deep into the earth to tap the heat resource.


Figure 8. Dominica has the second largest boiling lake in the world and thus this energy can be utilized to turn turbines and generate electricity. Image credit: Antoine Hubert.

Summary of Alternative Energy Sources for the Caribbean

The Caribbean can be summarized into several locals depending on climate and geography. In the Leeward Islands, you have those locals that are mountainous and geologically active and those that are flat. Both receive the same amount of trade winds. In the Windward Islands, you basically have mountainous, geologically active islands that receive alot of clouds and rainfall. In the Greater Antilles, all are mountainous but not geologically active in terms f geothermal heat. And Central America is considered mountainous, windy on one side and geologically active.


Figure 9. Summary of each island and territory's natural resources and which type of energy is most effective in getting the most out of renewable resources.

Summary

Over the past two decades Caribbean countries have slowly begin to acknowledge the need for alternative sources of energy with wind turbines in Grenada, geothermal plants propose for Dominica, Montserrat and Nevis and hydroelectric power in Belize. The topic of climate change, environmental concerns, rising oil prices and the abundance of natural resources are all reasons why we should explore these alternative ways of energy. There are still some more in-depth studies to be done to fully convince some Caribbean governments that green-energy is the way of the future and each will be addressed as my concern for sustainable energy for the Caribbean.

The next blog on this topic will look at how close we have come to integrating green energy into our economies.

References

Renewable Energy Options in the Caribbean
Alternative Sources of Energy for the Caribbean
National Renewable Energy Laboratory

Weather456

Weak tropical disturbance is expected to develop later this weekend; Eyjafjallajökull continues to erupt

By: Weather456, 12:37 PM GMT on May 16, 2010

The weather pattern over the Atlantic has not change much from since yesterday but has become a bit more convectively active. We still have an upper level trough in the center of the Caribbean with a very expansive upper level ridge/anticyclone to its east over the tropical Atlantic. This expansive ridge is aiding in the ventilation of thunderstorms associated with an active tropical wave approaching South America and the Southeastern Caribbean. This has allowed thunderstorm activity to expand with debris clouds spreading all the way to the Cape Verde Islands. There is a moderate to high chance that showers will reach the southern Caribbean on Monday afternoon, afterwhich, any associated shower activity becomes skewed as the tropical waves moves into South America later on Tuesday.

All of the reliable global models agree that the tropical wave will reach the Southwest Caribbean in 3-4 days and all have indicated that a broad area of low pressure may develop over the area by weekend. The models, however, differ on what will happen to this transient disturbance. The GFS, no surprise, deepens the system into maybe a depression, while the CMC thinks development will take place in the Eastern Pacific. The models agree that the system will remain weak and move into Central America by day 8-9.

I do believe that a broad area of low pressure will develop over the Southwest Caribbean but I highly doubt we will see significant development. First, a band of high shear lies just north of 15N which would tear anything apart trying to venture northward. Second, a sprawling ridge extending to the Gulf of Mexico will keep anything on a westerly course and into Central America. If the system manages to stay long enough in the Southwest Caribbean, then there is a possibility that some development may take place but the steering flow seems strong in 5-7 days in that part of the Caribbean.

I will continue to monitor for any changes.

Eyjafjallajökull Continues to Erupt



Figure 1. Transient cyclones continue to aid in the advecting of ash towards the United Kingdom. Image Source: EUMETSAT


Figure 2. Volcano in Iceland continues to hamper air service in the UK. Icelandic volcanic ash covers the sky of Britain. Civil Aviation Authority of Britain has closed on Sunday to 17:00 BST on time for flights in the airspace of several parts of Northern Ireland. Source: Image EUMETSAT


Figure 3. Volcanoes emit huge amounts of sulfur dioxide (SO2) into the atmosphere which is harmful to human beings and many other living things. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain. Using ozone detecting tools, satellites are able to measure S02 concentrations by volcanoes at 5KM. This image is valid 15 May 2010.


Figure 4. Not all effects of volcanoes are bad. Studies have shown that volcanic ash is actually good for marine life. When it comes into contact with seawater, volcanic ash releases large amounts of phosphate, iron, and other “macronutrients and ‘bioactive’ trace metals,” which can support microscopic biological life, like phytoplankton.

Phytoplankton are basically a type of marine "plant" and since they photosynthesize, they contain chlorophyll. By looking at high resolution satellite imagery, this chlorophyll can be detected by the greenish reflectivity.

Here we see phytoplankton blooms along the Icelandic south coast, likely thriving on the chemistry of volcanic ash.

Weather456

Tropical Weather Outlook: May 15-31

By: Weather456, 12:14 PM GMT on May 15, 2010

Tropical Update

I took a look at the water vapour imagery and infrared imagery this morning and a few features stand out. A non tropical convective low is moving over Texas bringing increases in shower and thunderstorm activity. Expect this system to continue off to the east across the Southern United States over the next 2-4 days with a cold front emerging around day 4. Rainfall accumulations could exceed 3 inches over Louisiana, Alabama, the Florida Panhandle and Georgia.

There is a very pronounce upper level trough sitting over the Caribbean basin and I don’t fully believe its a TUTT cell as yet since this was form due to the directional shear between an upper high over South America-Tropical Atlantic and another over the Eastern Pacific. Water vapour imagery shows the trough tapping into deep tropical moisture and advecting it across the Northeastern Caribbean where localised shower activity is being reported. Though, the amount of moisture is elevated so areas have only picked up less than an inch of rain per day over the past 3-7 days. Expect this upper trough to linger for the next 2-3 days and be replaced by the migration of an upper ridge northward.

The third feature of interest is a very active tropical wave near 50-55W south of 10N moving off towards the west. Infrared satellite imagery shows a high increase in convection along the wave. The wave is expected to bring an increase in shower and thunderstorm activity to Guyana, Venezuela and Trinidad and Tobago over the next 24-36 hrs. Convective precipitation totals should exceed 1 inch over the next 1-2 days.

I will be taking a closer look at the area north of southeast Cuba later this week as the GFS is hinting that a weak shortwave trough will shift west and induce an area of low pressure east of the Bahamas. None of the other models show this scenario and the GFS forms this low under extraordinary high vertical shear near the subtropical jet. It is unlikely that such a system will be tropical if it does form. I will have more updates on this as the week progresses.

Today marks the start of the 2010 Eastern Pacific hurricane season and more than likely this year seasonal activity will be affected by the expected increase in activity over the Atlantic. I do not normally forecast for this area unless of meteorological significance or pose a threat to the west coast of Central America and/or Mexico.


Figure 1. Water vapor depiction of several features over the tropical Atlantic this morning.

Tropical Weather Outlook: May 15-31

Introduction

The 17-day period ending May 31 2010 is expected to have a low-moderate chance of tropical development based on climatology, activity over the recent years, vertical wind shear, the MJO and sea surface temperatures.

Climatology

May is not a month we normally see tropical activity but over the past couple of years, systems were found forming in May on average every other year, about the same as the long-term average for June. Systems forming in May normally form in the Western Caribbean or offshore the Eastern United States where low shear is found between the subtropical and polar jet streams. May systems are also found to be baroclinically induced meaning there is some association with dying fronts, wind shear and upper level systems. Storms forming in May are normally a threat to the Western Caribbean and to a lesser extend the Gulf coast.

The El Nino Southern Oscillation (ENSO) and Vertical Shear

As someone nicely put it earlier this week, the Bureau of Meteorology in Australia delivered the obituary of the 2009-2010 El Nino event in their fortnightly ENSO wrap up. They indicated in their report that the major factors such as ocean temperatures, the Southern Oscillation Index (SOI) and tradewind values, suggest that conditions have returned to normal across the Equatorial Pacific. They have also indicated that further cooling is likely and based on current computer models; there is a 35% of La Nina developing over the next 6 months. It is more than likely that we will be entering the hurricane season under neutral conditions.

Vertical shear over the past 2 weeks of May continued to be lower than normal and this could be in response to 1) the atmospheric element of ENSO, 2) very warm sea surface temperatures which create upward and outward motion in the tropical atmosphere and 3) a very warm troposphere which promotes ridging in the upper layers of the atmosphere.

Though the anomalies maybe lower than the climatological mean, the initial values are still not conducive for tropical cyclone development and they are not expected to change much over the next 2 weeks over the Atlantic, Caribbean Sea or Gulf of Mexico. Some of the more reliable models show the subtropical jet remaining north of 20N, stretching from the Gulf of Mexico, across the Northern Caribbean and subtropical Atlantic. The models also show a gradually decrease in shear especially in the Caribbean due to the migration of the subequatorial ridge northward. Here is probably where you would find the best chance of any tropical development.


Figure 2. Vertical wind shear analysis by the GFS valid through 26 May 2010 showing the sub-equatorial ridge and subtropical jet stream which would deliver huge amounts of vertical shear north of 20N.

The Madden-Julian Oscillation (MJO)

Based on a number of observations it is clear that the MJO has been in a suppressive state over the past couple of weeks of May. Convection indices have been down and day to day water vapour loops show mostly dry air masses across the Caribbean and Atlantic. However, despite theoretical odds, the ITCZ remained more active than normal. There was one other direct result on sea surface temperatures that will be discussed in the next section.

Most of the long-range models show an upward pulse reaching the Atlantic at the very near end of the month, that is, from about May 25. I have speculate that the Global Forecasting System (GFS) maybe rushing the MJO and it has but the other models agree that the MJO will have some influence over the Caribbean and Atlantic later this month. The influence would most likely be in the form of increase rainfall rather than tropical cyclone development because the pulse is not that strong. However, history has shown that the MJO can help initiate early season development (Alma-Arthur 2008), and the GFS is showing development over the next 2 weeks, so we should still keep our eyes peeled.


Figure 3. Prediction of MJO-related anomalies with the blue shades indicating areas of favorable upward motion. Predictors are RMM1 and RMM2 on May 13 through 20 days.

Sea Surface Temperatures

Currently, there aren’t any areas across the Caribbean and Atlantic that cannot support a tropical storm or even a hurricane. Sea surface temperatures are running an astonishing 2-3C above normal over the entire tropical basin. This really increases the chance of tropical convection during the next MJO passage. Sea surface temperatures have cooled in some spots over the past 5 days and that is due to an increase in surface divergence caused by the downward force of the MJO. I expect as we get into the hurricane season that sea surface temperatures will continue to warm and offset any changes by the atmosphere, especially since the North Atlantic Oscillation (NAO) is expected to remain negative.


Figure 4. NOAA/NESDIS SST anomalies on May 13 2010 showing above average temperatures across the entire tropical Atlantic, including the Caribbean and Gulf of Mexico.

Steering Pattern

Steering pattern is rather typical of May and early June with a trough along the United States East Coast and ridging over the Atlantic Ocean. Any storms forming in the Caribbean will either move into Central America or be pulled north then east depending on the timing of frontal systems. May is the transition month between winter-spring time conditions and summer conditions so lingering frontal systems will influence steering of systems forming in the climatologically favourable area. As for the Bermuda High, its position is dictated by the NAO which favours a weaker than normal centralised position. The NAO will also continue to favour a southerly biased on mid-latitude storm tracks.


Figure 5. Forecast of the location where the 500 mb pressure surface will be at a height of 582 decameters (5280 meters). This height marks the approximate southern boundary of the jet stream and consequently storm tracks.


Figure 6. GFS 200 mb analysis of troughs and ridges in the upper levels through 24 May 2010.

ITCZ Position and African Dust

These two factors do not really affect development so early in the season due to their relevancy with the climatologically favourable areas. Nevertheless, I will comment on them. The ITCZ position in 2010 based on precipitable water anomalies is much higher than in 2009, higher than in 2008 and other years and about the same position as 2005. The major difference between this year and last year is the phase of the NAO which exerts a downward force on the ITCZ during the positive phase. The ITCZ should continue to climb under the negative phase of the NAO over the next 14 days which should allow more active waves to enter the Caribbean Sea rather than South America.

African dust concentrations remained locked up in Africa but as tropical waves begin to emerge more frequently we can expect this dust to enter the Atlantic. The lack of African dust over the subtropical Atlantic is another reason why sea surface temperatures are so high there. We can expect a second dust plume to emerge around May 19, add to the small outbreak that occurred yesterday. The implications on early season development will be minute since this is not a climatologically favourable area.


Figure 7. Left: TPW water anomalies of the equatorial tropical Atlantic over the past 5 years on May 10. Tropical preciptable water anomalies were used as a proxy for the ITCZ position from year to year. Lowest latitude was in 2009 and highest in 2010 and 2005. Right: The Navy NOGAPS total optical dept forecast (top) and dust concentrations (bottom) through 19 May 2010.


Figure 8. MODIS Aqua composite images taken on May 14 2010 displayed here using the power of Google Earth. Here you can clearly see the relationship between African waves and Saharan Dust.

Conclusion

There is a low-moderate chance of a tropical cyclone forming in the Atlantic basin during the last two weeks of May mainly because of climatology and the slow decrease of vertical shear. All other variables seem conducive for tropical development so the Atlantic still bears monitoring. While chances of tropical development remain low to moderate for now, there is a moderate to high chance of convective rains over the Caribbean and Atlantic due to the passage of the MJO. The best chance of finding development would be in the Caribbean Sea.


Figure 9. Composite summary of what to expect entering the hurricane season of 2010 with African Dust shaded (brown), areas conducive for development (green), the subtropical jet (double arrows), the subtropical ridge and polar troughs (single arrows) overlaid on the current sea surface temperature map. This map took me hours to make as every careful thought was placed in giving an accurate summary as possible. The love for tropical weather really inspires to drive myself to the edge.

Correction: The arrows around the subtropical ridge need to be reversed to anticyclonic.

Weather456

Other Modulators of the 2010 Atlantic Hurricane Season

By: Weather456, 7:00 PM GMT on May 14, 2010

I have already issued my 2010 Hurricane Season Outlook; predicting 16, possibly 17 named storms. In this report I stressed on several major factors which I found to have great influence over the activity during the hurricane season – the El Nino Southern Oscillation (ENSO)-vertical shear relationship, Rainfall over West Africa and Tropical Atlantic, the North Atlantic Oscillation and Mean Sea Level Pressure, Sea Surface Temperatures and Continuation of Above Normal Activity since 1995. However, there are other factors that one might want to look at to further illustrate the activity of this year’s hurricane season and we will look at one of them today.

Other Indicators

The Quasi-Biennial Oscillation (QBO)
The Indian Ocean Dipole and Sea Surface Temperatures over the Gulf of Guinea
200 mb Zonal Winds over the Caribbean
The position of the ITCZ

The Quasi-Biennial Oscillation (QBO)

The Quasi-Biennial Oscillation refers to the periodic changes in equatorial zonal winds between westerlies and easterlies in the tropical stratosphere with a mean period and height of 26-29 months and 30 mb, respectively. The QBO was actually discovered on two separate occasions. During the eruption of Krakatau in 1883, dust from the eruption took 13 days to encircle in the earth in an easterly direction near the stratosphere and the winds were consequently called the Krakatau Easterlies. Later in 1908, a scientist by the name of Berson, launched observational balloons above Lake Victoria in Africa and found westerly winds at about 15km (120mb). These westerly winds are called Berson's westerlies. Now we had two conflicting wind regimes in the lower stratosphere – the Krakatau Easterlies and Berson’s Westerlies.

In 1961, Reed and Veryard and Edbon resolved this conflict and showed that the winds over the stratospheric equator oscillate between westerly and easterly regimes. It was shown that the wind in the stratosphere changed direction on average every 26-29 months and that the alternating easterly and westerly wind regimes descend with time.

The link between the phasing of the QBO and tropical cyclone activity in the North Atlantic lies in its association with local vertical wind shear. The phases of the QBO tied to more (less) active hurricane season results in decreased (increased) vertical wind shear in the lower stratosphere. A westerly QBO (westerly anomalies in the equatorial zonal wind at 30 mb) during the Atlantic hurricane season, typically results in a more active hurricane season, with the exact opposite during the easterly QBO.


Figure 1. The 10-50hPa stratospheric zonal wind (upper) and typical variation when the 30 mb westerly winds are becoming stronger (wavy lines in grey shaded region) and Atlantic hurricane is theoretically enhanced. Hurricane activity is suppressed during the easterly wind phase of the QBO (lower unshaded region). Adpated from Gray - 1984.


Based on this information, you would expect hurricane activity to oscillate every 26-29 months or every two years. However, the data is not adding up. In the chart below, the easterly phase of the QBO occurred during the most active hurricane season on record, while the westerly phase occurred during two of the least active hurricane seasons last decade – 2006 and 2009. There were also large inconsistencies found also in the QBO 50mb and 30mb indices.

It was consistent during years like 2004 and 2008 where the phase was westerly.

There are number of reasons for such inconsistencies. For example, probably when the QBO was discovered and studied in the 1970s and 1980s, a period of low activity, it was useful for predicting year to year variations but now we are living in a period of high activity, it has become rather useless.

A second hypothesis is that the larger scale modulators of hurricane activity such as the El Nino-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Madden-Julian Oscillation (MJO), the Atlantic Multi-decade Cycle (AMO) and the Saharan Air Layer (SAL) have a greater influence over storm numbers and intensity.



Figure 2. 30 mb zonal wind composite anomalies for January to June of the years 2004-2009. Positive anomalies are the westerly phase, while negative anomalies are the easterly phase. The areas of most interest in measuring the QBO are over Indonesia and the Equatorial Atlantic Ocean, illustrated by the red boxes. While the QBO phases seem not to be directly related to storm numbers, the oscillation appears to affect number of storms developing south of 20N and east of 50W.

So we see here that storm numbers are not directly related to the phase of the QBO as some have suggested in the past. However, let us take a deeper look at this.

There was one correlation found to be associated with the QBO – Cape Verde-type systems. It was found that during the easterly phases, there were few tropical cyclones forming east of 50W and south of 20N. During the westerly phase, there was greater number of tropical cyclones forming in same region. This would explain why 2005 had so many storms, yet so little deep tropical activity and explain why 2006 had so little storms, but many deep tropical systems. In 2009, we had 9 named storms yet 4 of them formed west of 50W and south of 20N – Ana, Bill, Fred and Henri. The QBO seems to have greater control over vertical shear in the deeper tropics, while further west, the larger scale atmospheric circulations are greater modulators.

There were still some inconsistencies in this relationship but there some direct aspect to it.


Table 1. Relationship between the QBO phase and number of hurricanes and major hurricanes originating out of the deep tropics.

The 2010 Hurricane Season

The 30 mb zonal wind regime over the equator during January-April 2010 was easterly which would imply fewer storms in the deep tropics. This is a true possibility but a small one since all other modulators favor an above average hurricane season. This is something 2010 and 2005 have in common again, an easterly phase in the QBO. Though the possibility maybe small, don't be surprise that we end up with a season like 2005 rather than 2008 in terms of origins of storms. Remember the three big ones of 2005 - Katrina, Rita and Wilma formed west of 50W.

Since 2002, Dr. Gray and his team has discontinued using the QBO has a modulator in their December forecast. From since the December of 2003, they have put less emphasis on the QBO, along with West African Rainfall.


Figure 3. 30 mb zonal wind composite anomalies for January to April 2010, showing easterly wind regimes over Indonesia and the Atlantic Ocean. This would theoretically favor less hurricane activity but as we have seen with the inconsistencies in past years, this is expected to have little influence over seasonal numbers.

Summary

While the Quasi-Biennial Oscillation (QBO) was a useful tool in predicting tropical cyclone activity in its prime, inconsistencies over the past couple of years have shown it’s not an important modulator of total seasonal numbers due to larger scale modulators. However, there were some consistencies when comparing it to hurricanes and major hurricanes originating out of the deep tropics. The QBO was used at one point in my 2008 Hurricane Season Outlook but soon found the historical data to be inconsistent enough to use it as a viable tool. I expect the QBO to have a low-moderate influence on the distribution of storms in the upcoming hurricane season with a low influence on overall storm numbers.

Weather456

Investigating the North Atlantic Oscillation

By: Weather456, 9:21 PM GMT on May 13, 2010

The tropics remain quiet this afternoon and nothing is expected to develop over the next couple of days. My next blog will be on Saturday and will discuss what we can expect during the last two weeks of May 2010.

Investigating the North Atlantic Oscillation
January-April 2010

Introduction

The North Atlantic Oscillation (NAO) is a climatic phenomenon which is related to pressure fluctuations between the Icelandic Low and Azores High. Consequently, the variations in strength and position of these two pressure centers cause variations in the speed and orientation of the westerlies – the winds that lay between them. The NAO index or phase is calculated by comparing pressures at the Azores or Portugal with that of pressures in Reykjavik, Iceland.

A positive phase of the oscillation is characterized with a deeper than normal Icelandic Low and stronger than normal Azores High both at the surface and aloft. As a result, the pressure gradient over the North Atlantic increases and drives stronger westerlies. Due to the stronger than normal high pressure, the Polar Jet Stream is further north than normal due the blocking effects of the high. On the southern side of the strong subtropical ridge, trades are driven faster.

A negative phase of the oscillation is characterized with a weaker than normal Icelandic Low and weaker than normal Azores High both at the surface and aloft. As a result of the weak pressure gradient over the North Atlantic, the westerlies are weaker (minus mid-latitude storms) and the Polar Jet Stream is further south due to the shallow and weak blocking high. On the southern side of the weak subtropical ride, trades are driven slower.

The westerlies and polar jet stream dictates storm tracks and thus the oscillation is a major cause of winter/spring time variations in weather across the North Atlantic.


Figure 1. Conceptual model of the North Atlantic Oscillation and the climate effects during the two phases of the oscillation.

Weather

Positive Phase

A more northerly jet stream in the positive phase of the oscillation brings more storms into Europe resulting in wetter conditions there. Moreover, the warming effect of the Gulf Stream amplifies since we have more onshore flow from the Atlantic and thus conditions are warmer there. The positive phase of the oscillation brings wetter and warmer conditions to greater Europe and Western Asia. As storm tracks and rainfall shift north, drier than normal conditions develop over the Mediterranean.

The polar jet stream is higher and thus cold air remains in Canada and this effectively keeps the country colder than normal. However, because the cold air is locked up in Canada, we have few snow and cold outbreaks across the United States and conditions are warmer there. Moreover, southerly flow is increased as northerly flow is retarded which also causes further warming especially across the Eastern United States.

There are more storms in the positive phase due to the deeper Icelandic Low.

Negative Phase

During the negative phase of the Oscillation, basically the opposite occurs. The Jet stream shifts further south and so do storm tracks. Greater Europe is cut off from mid-latitude storms and the warming effect of the westerlies and thus areas across Europe remain colder and drier than normal. Further south, where the jet has migrated, the Mediterranean becomes wetter than normal.

As the jet migrates southward, cold air in Canada can flow southward leading to cold Canadian outbreaks across the United States with Eastern Canada becoming warmer than normal (no cold air locked up) and the Eastern United States wetter and colder than normal.

The Caribbean is less affected by such variations, due their position in the deep tropics, except for the intensity in trade winds which would amplify during the positive phase and weaken during the negative phase. The El Nino Southern Oscillation, which will see below, has greater influence over the Caribbean and possibly the North Atlantic Oscillation.

There are fewer storms in the negative phase due to the weaker Icelandic Low.

El Nino Southern Oscillation (ENSO)

An El Nino can actually cause or amplify the negative phase of the North Atlantic Oscillation due to the similar distribution of weather variations. During an El Nino, the polar jet stream dives southward, just as in the negative phase of the NAO. Thus, southern North America becomes cooler and wetter and northern North America becomes warmer. During the winter-spring of 2010, we had both an El Nino and a negative phase of the North Atlantic Oscillation and there is a possibility that the former caused the latter. Who knows, but it’s rather “lucky” and “too perfect” to have such conditions aligned, probably as clear-cut as the 2010 Atlantic Hurricane Season.


Figure 2. Regional impacts of warm ENSO episodes (El Niño).

January-April 2010

The North Atlantic Oscillation since January has been negative according to measurements taken at 500 mb, which is clearly evident from temperature, wind, rainfall, storm tracks, sea level and 500 mb pressure analysis.

Surface air temperature across North America was idealistic for negative NAO years with warmer temperatures over Eastern Canada and cooler temperatures over the Eastern United States. Greater Europe was colder than normal, cut off from the warming effects of the Gulf Stream and warmer temperatures were found further south along the Mediterranean.

Slightly warmer conditions were along the Eastern Caribbean due to weaker trades which would actually bring cooler conditions from up north from either cold fronts or the Canary current.


Figure 3. NCEP/NCAR composite surface temperature anomalies for the period January-April 2010.

Precipitation rates were also idealistic of a negative NAO. There were drier conditions long eastern Canada and Greater Europe, while wetter conditions across the Subtropical Atlantic, Southern United States and the Mediterranean. Drier conditions also dominated the Eastern Caribbean due to lack of cloudiness cased by El Nino.


Figure 4. GPCP precipitation composite anomalies for the period January-April 2010.

Storm tracked had an average latitude of 35N as oppose to 40-50N is positive and normal years. This is an indication of the jet stream position over the past 4 months and implies a negative NAO and/or El Nino.


Figure 5. 90-day storm tracks and precipitation from the Climate Prediction Center (CPC) ending 12 May 2010.

Sea level pressure and 500 mb heights were probably the most successful tool in assessing the North Atlantic Oscillation over the past months. We can see pressures in the Icelandic low were higher than normal and pressures near the Azores High were lower than normal. This implies a weaker Icelandic Low and weaker Azores High, the major characteristic of a negative NAO.

Mid-latitude storms are accompanied by low height pressure fields and we will see the significance of this in just a second. Heights near the Icelandic Low were higher and heights near the Azores High were lower. This could only mean that mid-latitude storms, which are accompanied by lower heights, shifted from north to south, as we see during the negative phase of the NAO.


Figure 6. NCEP/NCAR sea level pressure composite anomalies for the period January-April 2010.


Figure 7. NCEP/NCAR 500 mb pressure height composite anomalies for the period January-April 2010.

The last variable we will discuss is surface wind speeds. During the negative NAO, trades are weaker at the surface but westerlies are stronger near the subtropics because of the integrated number of cyclones which average wind speeds greater than 30 knots. This is actually one of the causes of such above average sea surface temperatures across the Tropical Atlantic per My 2010 Hurricane Season Outlook.


Figure 8. NCEP/NCAR surface wind speeds composite anomalies for the period January-April 2010.

Summary

By looking at a number of variables and comparing them to conceptual models, we can assess the state of the North Atlantic Oscillation (NAO) and its effects over the North Atlantic region. It is clear that we experience the negative phase of the oscillation over the past 4 months but because these conditions are similar to those experienced during warm episodes of ENSO as we experience during the same period, it is unclear whether the NAO was in natural phase or actually ENSO induced. One thing is for sure, is that the oscillation had noticeable climate anomalies over the North Atlantic and is one of the main factors for the upcoming hurricane season.

Further Reading

The North Atlantic Oscillation

The North Atlantic Oscillation - Wikipedia

Recurving Versus Landfalling Cape Verde Hurricanes

Weather456


5 Years of Blogging

By: Weather456, 5:22 PM GMT on May 13, 2010

It seemed liked only yesterday but July 23 2010 makes it 5 years blogging with Weatherunderground, which in my opinion, has the greatest forum on the Internet dedicated to weather and most importantly hurricanes. Over the past 5 years, I have connected with quite a few folks here, especially those who take the time to visit my blog each day. I have also posted quite a few topics and it's now at the point where it's necessary to create a reference to these blogs. That is exactly the focus of today's blog. The blog will be continually updated and is a link is provided to the right under recommended links. I think you would find them educational and interesting even if you have read them before. Enjoy!

Hurricanes and Tropical Storms

- Hurricane Dennis: One Year Later - 2006

- Hurricane Emily: One Year Later - 2006

- Herbert Saffir Dies at Age 90 - 2007

- Possible March Subtropical Development - 2008

- Understanding the Atlantic Hurricane Season: Technical Terms - 2008

- Anomalies in the ITCZ - 2008

- Tracking Caribbean Hurricanes - My Experience - 2008

- Understanding the Atlantic Hurricane Season: The SST Factor - 2008

- Tropics in May: The Transition Month - 2008

- First Tropical Waves (2004-2008) - 2008

- Forecasting Tracks of Cape Verde Hurricanes Using the NAO - 2008

- My Thoughts on NOAA 2008 Hurricane Season Outlook - 2008

- Hurricane Preparedness Week - 2008

- Tracking Tropical Waves - 2008

- Tracking Tropical Cyclones: Center Fix - 2008

- Gustav, Ike, Paloma and Alma Retired - 2009

- Understanding the Atlantic Hurricane Season: Vertical Wind Shear - 2009

- Patterns in the ITCZ - 2009

- Understanding the Atlantic Hurricane Season - the Saharan Air Layer - 2009

- Hurricane Preparedness Week - A Caribbean Perspective - 2009

- An Observational Look At African Dust in July - 2009

- Re-curving Versus Land-falling Cape Verde Hurricanes - 2009

- Did the NHC Drop the Ball on Subtropical Storm Grace? - 2009

- The Structure of a Tropical Cyclone - Microwave Imagery of Choi-Wan - 2009

- Met Office Glosea Model Performance for 2009 - 2009

- Understanding the Atlantic Hurricane Season: Tropical Jet Streams - 2009

- Tropical Cyclones: Physics, Energetics and Mechanics - 2009

- The 1502 Hurricane of the Dominican Republic: Columbus’ Hurricane - 2009

- Katrina's and Wilma's Youtube Video Tributes - 2009

Tropical Outlooks and Forecast Verifications

- 2008 Atlantic Hurricane Season Outlook - 2008

- 2008 Atlantic Hurricane Season Forecast Verification - 2009

- 2009 Atlantic Hurricane Season Outlook - 2009

- 2009 Atlantic Hurricane Season Forecast Verification - 2010

- June Outlook - 2009

- July Outlook - 2009

- August Outlook - 2009

- September Outlook - 2009

- October and November Outlook - 2009

- 2010 Atlantic Hurricane Season Outlook - 2010

Drought

- Texas Drought Situation - 2009

Flooding

- La Nina and MJO Floods Australia

- South African Floods - 2008

- Flooding in Brazil - 2009

- Brazil Continues to Flood - 2009

- Typhoon Morakot Record Rainfall - 2009

- The Power of Rainfall: Fred-ex and Typhoon Ketsana - 2009

Volcanoes and Earthquakes

- Ash Plume from Karymsky - 2006

- Behind the Samoa Tsunami - 2009

Heat

- How Heat Affects Us - 2006

- Historic Heat Wave Hits Western North America - 2009

Winter Weather

- Snow In Middle East But Global Warming Rages On - 2008

- Cold Weather From Siberia, Brrr! - 2008

- Canadian Blizzard - 2008

- Snow Causing More Trouble in China - 2008

- Storm Lashes the Western Coast of Europe - 2008

Seasons and Weather

- Summer is Here - 2006

- List of Natural Hazards - 2006

- Sexy Weather: Clouds -2006

- Air Quality At The 2008 Beijing Olympics - 2008


- LOL! A large self-destructing Palm Tree/My Hurricane Wilma Video - 2008

Climate

- Global Warming Myths and Facts - 2008

- January Highlights - 2008

- Southern Ocean Rising Due to Warming - 2008

- 2009 Vs 2004 - 2009

- Caribbean Coral Reefs and Climate Change - 2009

- El Nino and the Earth's Rotation - 2009

- The Southern Oscillation - 2009

- Record Low Global Tropical Activity - 2009

- El Nino and the Thermocline - 2009

Travel and Places

- Destination Barbados - 2008

- Destination Sydney, Australia - 2008

- Destination The Caribbean - 2008

- A Google Earth Tour of the Caribbean - 2009

- Saint Kitts/Nevis: History - 2009

- Saint Kitts/Nevis: Today - 2009

- Saint Kitts/Nevis Photo Gallery - 2009

Humor

- Can Britney Spears Help Stop Global Warming - 2008

- Hurricane Humor - 2009

Book Reviews

- An Earth Day Book Review: Encyclopedia of Hurricanes, Typhoons and Cyclones -2009

Other

- Solar System's Wild Weather - 2009

- About Weather456 - 2009

- Christmas Gift Ideas - 2009

Weather456

Tropical Update

By: Weather456, 12:17 PM GMT on May 12, 2010

Tropical Update

The overall atmosphere across the tropical Atlantic is unfavourable for tropical cyclone development over the next couple of days due to upper level westerlies and an abundance of dry air aloft. The lingering effects of the weakening El Nino is conjunction with the flow around the sub-equatorial ridge over Northern South America, is causing wind shear to run 10-20 knots above normal across the Caribbean region – a place where you would look for early season development. This flow is confluent in nature and is supporting dry air advection from about 600 mb. In addition to wind shear, the Madden-Julian Oscillation (MJO) appears to be suppressing convection across the Tropical Atlantic and except for a localise thundershower or two, widespread convection is limited north of 10N.

This pattern is expected to continue to atleast this weekend as leading long-range models foresee an upward pulse in the MJO from about an average date of May 16. I expect an increase in convection and moisture across the Western Atlantic later next week, particularly where sea surface temperatures are warmest, that is, Central America, the Greater Antilles and the Lesser Antilles, particularly the southern region. The Gulf of Mexico is not expected to benefit much from this upward pulse and moisture here will be diurnally-based (afternoon thunderstorms over Mexico) and mid-latitude based (lingering frontal systems over the Southern United States).

Upper winds might become a bit more favourable over the Caribbean as the ridge expands north in response to the upward pulses generated by convection. However, much of the global models show this to be a slow decrease over the next 5-7 days.


Figure 1. Water vapour imagery of the Western Atlantic showing the general upper level flow.

Currently, there are 5 tropical waves analyzed along the convective inter-tropical front but none pose a threat to develop due their relatively low latitude (south of 10N) and the fact that hostile conditions are just north of them. The main cause of such an active ITCZ is the presence of warm sea surface temperatures. Here, the upward motion of warm air is greater than the downward force of the MJO. There is one wave approaching 35W which is very impressive for May. Total precipitable water loops show this classic inverted-v and cyclonic curvature in the moisture field. An ASCAT pass from last evening revealed pronounce turning of the surface winds along the wave. Numerous clusters of convection are within 200 nmi east of the wave axis. Expect this wave to reach the southern Antilles by the beginning of next week, in line with the upward pulse of the MJO.


Figure 2. Visible satellite imagery of Africa and the entire tropical Atlantic, showing the first wave train of the season with the wave indicated by A, the tropical wave expounded on.

Publications Page

Publications such as outlooks and summaries are now available for download on one single blog page - the publications page. A link to the page is to the right under recommended links.

Weather456

Publications Page

By: Weather456, 7:10 PM GMT on May 08, 2010

A Look at Severe Weather Across the Southeast United States

- A powerpoint presentation of the formation and structure of severe weather across the Southeast United States, with background information applied to satellite, radar, model observations.

The 2009 Hurricane Season Forecast Verification (PDF) (Word 2007)

- Forecast verification of the 2009 Atlantic Hurricane Season, what actually happened versus what was forecast back in May 2009.

The 2010 Hurricane Season Outlook (PDF) (Word 2007)

- A look at the activity forecasted for the upcoming Atlantic Hurricane Season.

Weekly Tropical Weather Report - May 8 2010 (PDF) (Word 2007)

- Weekly tropical weather report with this week focusing on the first tropical wave of the 2010 Northern Atlantic Summer.

Tropical Weather Outlook - May 15-31

- A look at the activity forecasted for the last 2 weeks prior to the start of the hurricane season.

Weekly Tropical Weather Report - May 15 2010

- Weekly tropical weather report focusing on the downward motion of the MJO and the progress of El Nino.

Tropical Weather Outlook - June 2010

- A look at the activity expected during the first month of the hurricane season.

Weather456

Hi back again...

By: Weather456, 5:32 PM GMT on May 08, 2010

Hi this is Weather456 back for another hurricane season but instead of a daily blog like last hurricane season, you would be able to download my publications available in pdf, word and powerpoint presentations to help guide through the upcoming active hurricane season. I will not have time to be on the blogs hour after hour but will more than likely answer all questions through WU emails and blog comments. Here is a list of upcoming publications, just return to the blog and the links will appear as available.

The 2009 Hurricane Season Forecast Verification

The 2010 Hurricane Season Outlook

Weekly Tropical Weather Report - May 8 2010

A Look at Severe Weather Across the Southeast United States

Weather456


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Weather456's Tropical Weather Blog

About Weather456

With a Bachelors Degree in Environmental Sciences (2009), began tracking tropical storms in 2002 and is now a private forecaster.