Weather456's Tropical Weather Blog

Historic heat Wave hits Western North America; Tropical Update

By: Weather456, 10:42 AM GMT on July 30, 2009

Unseasonable warm temperatures continue to plague portions of western Canada and United States causing some areas to push record temperatures over the past week. Currently areas along Western North America are experiencing a heat wave, which is a prolong period of excessive hot weather. I live in the Caribbean which normally experiences high temperatures year round and I normally look at areas to the north for a more cooler climate, so you bet I was interested to see temperatures higher than here in tropics, especially in Canada.

Figure 1. Surface temperatures recorded yesterday, July 29 at 7PM EDT or 4PM PDT around the diurnal temperature maximum.

In the Pacific Northwest, areas that normally accustom to the wet weather and the cooling effect of the ocean during summer recorded their hottest temperatures in history. The National Weather Service (NWS) in Seattle, Washington recorded 102 degrees Fahrenheit around noon yesterday, breaking the old record of 100 in 1941. Meanwhile, Portland ventured into its third day of triple-digit heat Wednesday, hitting 104 degrees by midday. If the forecast is correct, there is a slight chance the city could reach or even surpass its all-time high of 107 degrees, hit four times, most recently in 1981. This is the 5th consecutive day of warm weather across the Pacific Northwest and it is expected to continue for atleast the next day or two, which has led to numerous heat and fire advisories.

The record heat is also being felt in Canada, where on July 28; Victoria, British Columbia reached a record high of 91F beating the old record of 84F set in 1958. Even higher temperature records were set in Port Alberni, which reached 102 degrees, which is shy of the record high temperature of 107 set back in 1926. The highest temperature recorded across Canada during the past day or two was 104 in Lillooet.

Pardon my French, but these temperatures bring new definition to the phrase “Hell on Earth”. The cause of this hot weather is not surprisingly, a stagnant deep layer ridge across Western North America that is 1) blocking the normal west to east flow, suppressing cool onshore flow and 2) increasing warm southerly flow into the region. The latest GFS model run show this ridge of high pressure not leaving anytime soon, the earliest being Saturday, so continued high temperatures are in the forecast for the remainder of the week.

Table 1. Record high temperatures recorded at several locations across Western North America during the past 2 days. Credit: United States Weather Service and Environment Canada.

As with any heat wave or summer event, air conditioners, ice related foods, public water facilities and shade will be in high demand. Due to the increase in demand for electricity that power air conditioners, a power surge may lead to electrical outages, which would further worsen the situation. Other effects of heat waves include danger from wildfires and actual damage to infrastructure. In July 2006, I posted a blog on “How Weather Affects Us: Heat” which outlines some of the dangers of excessive heat and what precaution can be taken to prevent dehydration and overheating. Heat kills more persons each year than storms do.

Figure 2. GFS 850 mb temperatures with the upper level flow overlaid valid through 1 August. Credit: Unysis Weather

The weather for July has been particularly unusual for summer, especially when unseasonable cool temperatures dipped south across the Eastern United States, also add to the low July tropical cyclone activity. Weird.

Are any climatic factors involved?

Global warming advocates will likely use this event as fuel and I would not blame them since these are historic temperatures. However, I’m not too well educated on the topic of Global Warming and Heat Waves, but I plan to have a blog on whether heat waves have been increasing over the past 5-10 decades. Another factor that is closely tied to the heat in the upper western portions of North America is El Nino. During El Nino years the polar jet stream becomes absent across the northwest United States and British Colombia as it shifts to areas further south. Storm tracks shift in tandem with the jet, which reduces the west-to-east cooling effect and causes warmth to build across the area.

Tropical Update

The tropics remain quiet this morning with one particular area of interest in the Eastern Atlantic. A tropical wave is estimated to be located near 31W south of 15N moving west near 15 knots. Showers and thunderstorms have increased along the feature but is mainly confined to the ITCZ. Last night QuikSCAT showed a broad area of low pressure associated with this feature near 30W with excellent inverted V amplification. The feature is currently moving through a marginally favourable environment with shear near 5-10 knots, sea surface temperatures near 27-28C but rather dry air directly to its north. Dry air will probably be the inhibiting factor here but the latest SAL maps show dust is dispersing so we will have to see how things develop with this wave. The models believe that the atmosphere will remain dry and stable as the wave moves west and little development expected. However, some of them did show the wave north of the Antilles on Monday, and then near the Bahamas by Wednesday, which means some amplification is going on. In my opinion, I feel this wave will continue west with some chance of development, but that chance is currently low with the main deciding factor being how stable/unstable the atmosphere becomes.

There is a second strong wave about to emerge over the Atlantic and that fairs a better chance since Sal has more than disperse ahead of it. All these features will be watched.

Folks in Hawaii may want to watch Tropical Invest 97E located towards the southeast. Recent satellite imagery showed a well organize disturbance with excellent banding and upper anticyclonic outflow. Along with the upper environment, sea surface temperatures remain near 27-28C just favourable for topical development. The last GFDL model run show the system passing south of the Big Island but close enough for the outer bands to bring rain to the island. The system will likely be re-designated as a Central Pacific Invest later today as it passes 140W.

In other stuff, it was last night I discovered I was a featured blogger, and I would like to say thank you too all the congrats and as I said in my 250th blog post, looking forward to the future.


Record Low Global Activity

By: Weather456, 10:26 AM GMT on July 28, 2009

The three tropical waves mentioned yesterday have change little over the past 24 hrs. There is however, two additional strong waves near 15E and 30E. These waves will emerge one behind the other later this week and next week, with each paving the way for the other. It is likely that August will not go without a named storm. My August Outlook is schedule for either Saturday or Sunday.

Record Low Global Activity

July 2009 will likely go down as one of the most inactive months in the past 30 years, not just in the Atlantic but the entire Northern Hemispheric tropics. The Accumulated cyclone energy (ACE), which measures the activity of individual cyclones and cyclone seasons, was about 15 as of Typhoon Molave on July 19, well below the average of 70 for the month of July!

Most tropical cyclones that develop in the Northern Hemispheric tropics normally occur between May and November when sea surface temperatures and convective activity are at their climatological peak. Normally, activity increases from West to East, that is, the Western Pacific basin is more active than the Eastern Pacific Basin, which is more active than the Atlantic Basin. According to the Joint Typhoon Warning Center (JTWC) and the National Hurricane Center (NHC), total tropical storms as of July 27 were 7, 4 and 0 respectively.

When was the last time we had such low activity?

The last time we had so little activity was in 1977, more than 30 years ago and ironically, the May-June-July period for that year is about the same as the May-June-July period for this year. This is what Wikipedia said about the year 1977 and I quote:

“The 1977 season was very inactive, with only 6 named storms. The Atlantic basin was not alone in this inactivity, though; the 1977 Pacific hurricane season was also inactive as was the 1977 Pacific typhoon season. The cause is unknown.”

Figure 1: Total Accumulated Tropical Cyclone (ACE) energy for the Northern Hemisphere for May-June-July. This three-month ACE sum is the lowest since 1977. Credit: Ryan N Maue, Florida State University.

Which basin is currently the most inactive thus far?

Table 1 shows the current ACE, the yearly average, the average through June 30, and July 31 and July average. The largest difference between actual and what is expected for July 31 occurred in the Western Pacific and this is no surprise since it is normally an active basin and anything less is noticeable. The Eastern Pacific is also well below the normal ACE through July 31 with the Atlantic having the smallest difference due to the fact that thus far the basin is normally quiet.

Table 1. Global Tropical Cyclone ACE valid July 28, 2009 00Z, showing most basins where below their climatological values. Credit: Ryan N Maue, Florida State University.

What is causing such low activity?

The causes are just as unknown as in 1977, but we have a bit more tools to give us an idea of what is occurring in 2009. We often here that cyclogenesis depends on several features such as warm sea surface temperatures, low vertical shear and high relative humidity and instability. However, we often neglect the last ingredient, a pre-existing disturbance with sufficient deep convection. In a publication titled “Introduction to Tropical Meteorology”, it stated that this last factor has proven over previous years to be the most important. Have these pre-existing disturbances been relatively absent or weak this year? The answer is somewhat and the culprit is none other than the Madden Julian Oscillation (MJO).

The Madden Julian Oscillation (MJO)

The MJO is a wave-like planetary disturbance that travels across the globe enhancing tropical rainfall. During the positive (negative phase), tropical convection is enhanced (suppressed) and the likelihood of tropical cyclone activity is increase (decreased). According to some recent MJO updates by the Climate Prediction Center (CPC), the MJO signals have been weaker than normal over the past 2-3 months. The suppressive states are also lasting longer and more pronounce that the enhancing state. This is likely causing the lack of convective activity in the tropics, which is the first step in tropical cyclogenesis.

Figure 2: Outgoing long-wave radiation (OLR) which is a proxy used to measure tropical cloudiness. High (low) values of OLR signifies less (more) cloudiness. High OLR values were observed across much of the tropical Atlantic and Pacific basin with the exception of near the Philippines, which was a result of multiple tropical cyclone tracks. Credit: NOAA Climate Prediction Center

Vertical shear and sea surface temperatures have become somewhat corporative across all basins but this downward motion in the MJO has continued to preclude any tropical development. This interesting discussion came up in the San Juan Puerto Rico area forecast discussion at 2:05 PM AST 27 July:

“Moreover, the latest 24-month running tropical cyclone accumulated cyclone energy /ace/ index for the northern hemisphere shows the lowest sums in nearly 30 years. What this means is that while the local environment may allow for a tropical cyclone to sustain itself...the overall tropical environment has precluded one from actually forming at this time.”

This is only one theory to describe the inactivity in the Northern Hemispheric Basin as other tropical disturbances and cyclones has fell to other environmental variables – Hurricane Carlos (cool SSTs), Tropical Storm Dolores (high shear) and numerous tropical Atlantic waves, African dust. However, the suppression of tropical rainfall over Africa is likely causing this increase in African dust and subsidence is increasing the high pressure, which is driving the dust west.

La Nina

The second cause was proposed in an article entitled The Great Depression! Tropical Cyclone Energy at 30-year lows by Ryan N. Maue at the Florida State University which stated that the tropical atmosphere cooled during the past 2 years due to the 2007-2009 La Nina. This is not surprising since the La Nina of winter 2007-2008 brought some of the coldest temperatures to Saint Kitts, first snow in Iraq and one of China’s largest snowstorms in almost 40 years. This has led to a suppression of tropical activity worldwide during 2009.

Solar Cycles

On 2 January 2008, the Space and Science Research Center (SSRC) issued a press release stating that the sun’s surface flow has slowed and we are entering a solar minimum. They stated the records of sunspot counts over the past 6000 years show that anything lower than 50 means an intense cold climate. This could potentially be one of the causes of cooler tropical oceans but since there is little known about the relationship between hurricane frequency and sun spot counts, this theory unfounded.

What does this mean for the Atlantic Hurricane Season?

It is hard to say, but if the current trend continues, the season might be similar to 1977, which had 6 named storms. However, we have no idea of whether this trend will continue and in 1977, 5 of those storms became hurricanes with Anita the most notable. In addition, 1977 lay in the decadal period of low inactivity whereas 2009 lies in a period of high activity for the Atlantic basin. In other hurricane seasons where the May-June-July ACE have been low was 1988, 1998 and most recently, 2007. All these years and 1977 featured a retired category 5 hurricane (Anita, Gilbert, Mitch, Dean and Felix). This is due to the fact that accumulated potential energy that builds in the atmosphere is not being evenly distributed.

In Conclusion, for the period May-June-July 2009, record low activity has been recorded for all basins in the Northern Hemispheric tropics. There are currently three theories put forward to explain this current inactivity but we have no idea if it will continue, especially into the peak of the Atlantic Hurricane Season.


Reality of Three African Waves

By: Weather456, 10:36 AM GMT on July 27, 2009

There are three African waves that I am watching this morning across the central and Eastern Atlantic. The first wave is located near 40W south of 15N moving towards the west near 20 knots. Satellite imagery and TPW loops continues to show deep cyclonic turning along this wave axis and this is supported by QuikSCAT, which shows a broad surface circulation with the wave. Convection along the wave remains weak and scattered but clustered around a central location due to dry air to the north. The models do not develop this wave but the GFS briefly develops a low pressure along the feature over the next day or two and then drops it. For development to occur the wave would have to slow down, overcome dry air and build convection, this seems likely as the wave nears the islands later this week.

The second wave just emerged and is located along 18W south of 15N moving west near 10-15 knots. This wave is just as define as the previously discussed wave but possesses more convection and lacks a close low level feature. This feature is doing well considering it is surrounded by a layer of African dust and the 06Z GFS thinks it has potential for some development.

The last African wave is located over the continent itself and is expected to emerge on Friday at which point most models show a broad area of low pressure near the Cape Verdes.

All these features present the potential to develop if they can battle dust over the next week and thus will be watched as they head west. One should keep in mind that the GFS is predicting an active month in terms of African waves.


The Southern Oscillation Index; Tropical Update

By: Weather456, 11:33 AM GMT on July 26, 2009

The Southern Oscillation Index

The Southern Oscillation Index (SOI) is basically a measure of the atmospheric component of the El-Nino Southern Oscillation (ENSO). The Southern Oscillation (SO) is the difference between sea level pressure at Tahiti in French Polynesia and Darwin in Northwestern Australia. The SOI is the difference between the normalize sea level pressure anomalies between the Western and Eastern Pacific.

La Nina

During La Nina, pressures are normally higher in the Eastern Pacific and lower in the Western Pacific. When the SOI is persistently positive, it indicates there is higher pressure in the Tahiti region and that lower pressures over Northern Australia are further from the International Date Line. This higher than normal pressure help increase the easterly trades at the equator, resulting in upwelling of cool waters due to divergence and typically results in the onset of La Nina.

El Nino

During El Nino, roughly the opposite occurs as a negative SOI indicates lower pressures near Tahiti and the lower pressures over Northern Australia are nearer to the date line than at Darwin. This lower than normal pressure effectively decreases the trades which aid in the development of equatorial westerlies. This further reduces upwelling and transfers heat energy from the Western Pacific to the Eastern Pacific, which leads to El Nino.

Figure 1. Schematic view of the Southern Oscillation during La Nina and El Nino events.

Figure 2. Tradewind and precipitation cycles between La Nina and El Nino events.

Figure 3&4 show some past ENSO events in relation to the Southern Oscillation Index. In most El Nino years, the Southern Oscillation has persistent negative values and vice versa for La Nina years.

Figure 3. Southern Oscillation Index, 1993-2000.

Figure 4. Southern Oscillation Index, 2007-present


In some cases, the Southern Oscillation Index is affected by mid-latitudinal and local scale events, which causes the index to be unreflective of equatorial sea surface temperatures. For example, sea surface temperatures continued to rise across the equatorial Pacific up to mid-July, yet the SOI has been positive for the past 2-3 weeks; which is a contradiction of events. This is likely due to warmer SSTs along the coast of Australia, which resulted in lower pressures at Darwin and recent mid-latitude flow in the Southern Ocean, which resulted in, increase flow and strengthening of the high pressure zone near Tahiti. If El Nino continues to intensify as forecasted, then larger scale effects will take hold. There is another index called the Equatorial Southern Oscillation Index (ESOI) which effectly only measure patterns in the equatorial region thus eliminating noise from mid-latitudinal effects. Nevertheless, the reponse of the SOI is an indicator that El Nino is not particularly strong at the moment.

Figure 5. 850 mb wind anomalies through 22 July showing above normal easterly trades due to higher than normal pressures near Tahiti. This pattern is typical of La Nina events despite warming in the equatorial Pacific which inidates El Nino.

This is part 2 of a series of El Nino-orientated blogs. The previous read discussed how the Earth’s Angular Momentum (Earth’s Rotation) and ENSO are linked. The next part will discuss the Upper Ocean Heat Content and Thermocline.

Tropical Update

Most of the tropical Atlantic and Caribbean remain under the influence of dry air and a layer of Saharan Dust, thus much of the convection is confined to the ITCZ, which is near 10N. There are two clusters, which caught my attention; one at 30W and the other near 50W. It is likely the latter wave will not develop but the tropical wave at 32W might have potential to develop if it was able to build convection. Last night QuikSCAT showed this feature possesses a mid-low level circulation, but convection remains scattered along the axis. The modes do not develop any of these waves but they will be watched as they head west.

There is another area of convection across South-eastern Mexico being enhanced a passing tropical wave.

The tropics will likely remain quiet for much of this week. The next likely chance of development is a series of strong tropical waves that will emerge during the course of this week and next week.


Tropical Update; 92L revisted

By: Weather456, 1:03 PM GMT on July 25, 2009

The tropics remain quiet this Saturday morning except for a possible tropical wave approaching the islands. Showers and thunderstorms have increase in association with the ITCZ just a few hundred miles east Trinidad. Satellite imagery showed this feature maybe associated with unanalysed tropical wave along 52W. There is turning evident along this feature based on visible and QuikSCAT imagery but no evidence of a circulation trying to form. The system is moving over 10 knots of shear with a ridge expanding northward in tandem with the ITCZ. This should allow a somewhat favourable environment as the feature straddles west. None of the models develops this feature but some show some increase moisture as another tropical wave at 40W enters the region by Sunday. Regardless of development, there is a fair chance of showers spreading into northeast South America, Trinidad and the Windwards over the weekend.

There are no other areas of interest, but this might all change by the first week of August, where for the first time the GFS develops an African wave and keeps it closed as it tracks across the tropical Atlantic.

Subtropical Invest 92L

This invests occurred on the 1st day of the hurricane season, which showed remarkable subtropical characteristics at its peak of organization and intensity. Below you download the Tropical Cyclone Report of 92L, which I created. There is also a link to Tropical Invest 90L, which was completed late last month.

Tropical Invest 90L
Subtropical Invest 92L

My August outlook is schedule for next weekend and if the GFS keeps the Cape Verde System by then we may have an interesting start to August.


Ex-98L affecting the Northeast; Tropics Quiet

By: Weather456, 10:29 AM GMT on July 24, 2009

Subtropical Invest 98L

Invest 98L was designated yesterday morning, but was quickly dropped after the feature became tied to frontal boundaries. However, this did stop the system from bringing high wind, rough surf and heavy rains to part of the northeast yesterday and early this morning. This system was likely non-tropical, maybe subtropical at one point, but because a large amount of tropical moisture was involved, the system did not appear so on satellite and radar imagery.

As the system moved towards the north-northeast, it deepened only gradually but because there was a weak high to the north of the system, it helped generate a pressure gradient that produced gale force winds. Much of these winds and rain remained mainly offshore the Jersey coast as the system tracked to the east, but as a result, the onshore flow was directed at Long Island, Rode Island and Cape Cod. Several locations reported gusts in excess of 25 knots with the highest at West Hampton Beach, New York. Some of the highest reported swells was by buoy 44065 (9.1ft) at the mouth of the New York Harbour and radar estimates were as high as 6-8 inches.

Currently the system is located just offshore Long Island, brining high wind, rain and surf to areas further north long Rhode Island, Massachusetts and Maine. The system should continue towards the northeast and affect Nova Scotia before heading out to sea.

Table 1. Selected surface observations between 23-24 July 2009.

Figure 1. New York City, Storm Total Surface Rainfall Accumulation Range 124 NMI.

Figure 2. Radar loop of the Northeastern United States.


I am still watching the left over trough from to the south of 98L, which the GFS is hinting may retrograde back towards the Southeast United States.

The GFS and CMC are inconsistently developing an East Atlantic wave. There are a few waves out that do have vigorous mid-low level flow and thus will be watched as we enter a favourable pattern in the Atlantic. Currently, nothing is showing signs of developing in the near term.


Developing East Coast Gale; 250th Blog Post

By: Weather456, 10:35 AM GMT on July 23, 2009

The area of low pressure that was expected to develop offshore the southeast United States still has a chance of becoming subtropical but a slim one. Most models have now trended from initially tropical/subtropical development to non-tropical develop as the feature interacts with an advancing frontal boundary.

Genesis of an area of low pressure will likely be offshore the Carolinian Outer banks over the next 12 hrs. Thereafter, the low pressure system is expected to travel north-northeasterly and intensify while remaining offshore the mid-Atlantic States. By Friday morning, the motion should bring it either close or near to Cape Cod, Massachusetts, then moving ashore over Nova Scotia by Saturday.

Now, a good amount of tropical air is involved in genesis and so this feature may carry some warm-core characteristics with it. For example, the rainfall and wind pattern displayed by models is symmetric to the east of the area of low pressure, which is dissimilar to non-tropical lows. In addition, most models show this feature remaining a shallow warm-core system over the next 24-36 hrs before becoming extratropical in 48 hrs. Thus, the impacts from this developing gale will be similar to the extratropical transition of tropical cyclones.

Asymmetries in the rainfall and wind around the low pressure area will cause much of the wind and rain to remain offshore North Carolina and Virginia coasts. However, as the storm intensifies and move north-eastward, the gale force winds begin to impact the coasts of New Jersey, New York, Connecticut, Rode Island and Massachusetts, generating swells near 6-10 ft. Small craft advisory in effect for some the inlets and bays of the mid-Atlantic coast. There is also the possibility of tidal flooding due to the fact the low pressure coincides with astronomical high tide. Last, moderate to heavy showers expected, and some places could get 2-4 inches of rain. Much of this rain as mentioned before will remain offshore the Carolina and Virginia coasts until reaching the mid-Atlantic states further north.


The surface trough extending from the developing gale system will continue to linger north of the Bahamas later today and will be watched for development as it drifts east.

A disorganize tropical wave is currently approaching the islands. This wave exhibits excellent inverted V pattern with scattered showers within 120 nmi of the axis. None of the models develops this feature but shear is expected to be somewhat favourable in the Caribbean Sea so the area will be watched. Regardless of development, scattered showers and isolated thunderstorms are expected across Trinidad and Tobago, Northeast Venezuela and the Windward Islands later today.

250th Blog Entry on the 4th Anniversary

This blog entry is my 250th, and coincides with my 4-year anniversary on Weatherunderground. In all I have posted about 15000 comments and made many friends since my stay here, which began July 23 2005. Here I would like to thank all who visits my blog regularly and hope you stick around over the upcoming years as I strive for 1000 blog entries, Gods willing.

NB: If I post an entry every day from tomorrow, I would reach 1000 around July 2011, lol.


97L dumps heavy rains; genesis of a new invest

By: Weather456, 10:18 AM GMT on July 22, 2009

Tropical Invest 97L continued to dump more rain across the Eastern Caribbean yesterday as it continued west. Heavy squalls brought gusty winds and heavy rains to Puerto Rico and the Dominican Republic yesterday with most locations picking up 3-5 inches of rainfall. This morning satellite imagery showed 97L continues to produce heavy showers across Hispaniola this morning and this could lead to a moderate to severe threat of flooding as up to 5 inches expected across the mountainous slopes of the island. Tropical Invest 97L, according to the Tropical Rainfall Measuring Mission (TRMM), has dumped up to 4 inches of rain over the 2-day period ending 0300Z this morning across the entire Eastern Caribbean from the Windwards to Hispaniola, and likely did cause some flooding in the islands. I expect these tropical rains to head towards Haiti, Jamaica and southeast Cuba later today and on Thursday. These areas can expect up 1 inch of rain with gusty winds in isolated squalls.

An area of low pressure just to the east of Florida has one of most interesting genesis since 90L back in May. An upper low over Florida continues to induce showers along a surface trough to its east. As a result, the area remains broad and under southerly shear of 25-30 knots, so little development expected today. However, by Thursday or Friday, the upper low is expected to either seclude or weaken allowing a ridge to take over. This should effectively lower vertical shear and allow for the development of a surface low along the trough. Currently, satellite imagery did not show any signs of a possible low level feature forming and though pressure remains high in the area, they are falling, indicating some gradually development is taking place. Showers have also become organize reminiscent of the pre-Hurricane Alex in 2004. Most of the global models develop this system but most are thinking the area will be subtropical in nature. They are in close agreement that this area will lift north-northeast ahead of a frontal trough bringing the feature close to the Outerbanks of North Carolina. There is a good chance that something tropical or subtropical may form over the next 2 days. A hurricane hunter flight is on standby for Thursday.

Elsewhere, a tropical wave approaching 50W south of 14N has increase in shower activity this morning. Currently upper winds are not conducive for development but locally heavy showers should move into Northeast South America and Trinidad later tonight and on Wednesday.


97L Moves though the Antilles; Possible development offshore SE USA

By: Weather456, 10:26 AM GMT on July 21, 2009

Tropical Invest 97L moved through the Southern Antilles yesterday bringing heavy squalls and gusty winds to the region. The wave is currently located at 65W, south of 23N with scattered convection within 200 nmi east of the axis. Much of this convection has left the islands and is now moving towards Puerto Rico and the Dominican Republic. However, some lingering moisture may enhance a shower or two later today. The table below shows some of the weather experienced in the islands on Monday as 97L pass through. The highest reported gust was near 39 mph with most stations reporting less than an inch of rain.

Showers and thunderstorms have clustered over the Bahamas this morning, associated with surface speed convergence aided by upper diffluence. All of the reliable models (even the GFDL) are showing the development of a surface trough of low pressure over the area. Some are also showing the northern section of 97L may aid in the genesis of such a trough. This trough will then move towards the NW towards the Florida Peninsula, but then eventually turn NE and ride up along the US East Coast ahead of a frontal trough. Development will be mainly determined by how much time this feature remains over the Peninsula, if it does at all. Currently, the region is under 10-20 knots and this is expected to become a little more favourable over the upcoming days. I suspect this will be our next invest (i.e, if it's genesis is mostly independent of 97L). Regardless of designation or development, increase in moisture surge for the Bahamas and Florida later today and on Wednesday.


Tropical Invest 97L heads for Windward Islands

By: Weather456, 10:57 AM GMT on July 20, 2009

The once well-organize tropical invest, 97L, has fell under a bit a vertical wind shear as it continues to heads for the islands. This morning satellite imagery showed the disturbance producing clusters of deep convection in and around the mid-level circulation. Satellite imagery also shows asymmetries in the cloud cover that suggest the system is being affected by some westerly shear south of an upper low over the Atlantic. Significant development of this system is not expected during the next 24 hrs as it heads west.

However, this is not the end of the invest. Upper winds might remain marginally favourable for now but could become favourable once the area enters the Caribbean Sea, thus it remains a feature of interest. Regardless of development, heavy squalls and gusty winds are likely to begin to affect the Barbados and the Windwards later today.


A tropical wave along 75W south of 23N is moving off towards the west near 10-15 knots. Much of the global models, including the NHC guidance show a surface trough developing over the Bahamas, later this week and head towards the northwest. Some models show this feature interacting with a frontal trough to produce a surface low that moves northeast along/offshore the Eastern Seaboard. Regardless of development, an increase in tropical moisture is expected to surge north across Cuba, the Bahamas and the Florida Peninsula later mid-week.


Typhoon Molave; Carlos' Hot Towers; Tropical Update

By: Weather456, 10:34 AM GMT on July 19, 2009

Typhoon Molave Makes Landfall

Typhoon Molave moved shore early Sunday, local time, brining heavy rains, high winds and rough surf to Southeast China. The storm was upgraded to a 75 mph typhoon shortly before landfall according to the Joint Typhoon Warning Center. The typhoon eye’s came ashore around 00:50 local time or 16:50 UTC bringing gusts as high 90 mph. The hardest hit area was Nanao town in Shenzhen City of Guangdong where the storm had landed. In Hong Kong, they reported a maximum gust of 61 mph as the center passed north of the city.

The onshore flow north of the storm produce 6-8 ft seas over the South China Sea, which affected the adjacent coastline. In Hong Kong, the harbour was generally spared since they were found in the offshore flow is the storm. However, the state’s hydrometeorological center indicated that several inches of rain fell across the region and that flooding was possible as the system continues island. As of this morning, there were no severe reports of damages as yet.

This storm killed at least 5 people on the Philippines on Friday as more than 20 inches of rain fell across the northern island of Luzon. Widespread flooding was triggered on this main island of the Philippines.

Figure 1. Canton radar imagery showing the storm during landfall around 00:48 Beijing time. Credit: China Meteorological Center

Hurricane Carlos

TRMM’s Precipitation Radar (PR) was able to see through the cloud canopy and reveal a 3-D structure of last week’s Hurricane Carols in the Central Pacific. One the most interesting features than stand out is what we call “hot towers” which basically are large cumulonimbus clouds. These hot towers form when surface air converges and rises, condensing to release heat and moisture. They are raised higher as the vertical velocity or speed of the inflow becomes stronger after each feedback loop. The number of hot towers a storm possesses has been used to predict if the storm would intensify or not, as these hot towers serve a focal point for intense updrafts at the center of a tropical cyclone. Hot towers are also known to have pierced the tropopause, at about 15 km.

Figure 2. A vertical view using data by TRMM Precipitation Radar (PR) taken Juy 13 0054 UTC. Credit: NASA

Tropical Update

I continue to monitor an area of disturbed weather located near 50W, just to the east-southeast of Barbados. Satellite imagery this morning, revealed this feature continues to possesses a well-define mid-low level circulation and maybe organizing as it redeveloped heavy thunderstorm activity as it enters warmer sea surface temperatures and a moister airmass with premature convective bands evident. As you may remember yesterday I posted an update on indicating that even though 97L had little shower activity it was suspected to go though the same faith as the wave near the Antilles. However, the difference between the wave at 65W and Ex-97L is the upper level environment. Shear is about 5-10 knots above the disturbance and expected to remain in that range for the next day or two. As the disturbance enters the Caribbean, shear depends mainly on an upper ridge building over the area and the invest’s motion. If the ridge should not build far enough north, the system could be affect by northerly shear in the Southeast Caribbean and hinder development of the feature. However, if the system was to remain on its westerly path it should avoid much of the higher shear to the north regardless of how long it takes the ridge to build and the TUTT to move out. Most of the global models are in favour of a fast building ridge. If the storm continues to persist through the day, I suspect a re-designation of 97L.

Though development is pretty much 50/50, track is a bit more evident. The storm is currently moving west and has slowed down some since about 24 hrs ago. On this current path, it should bring it near the Windward Islands and Barbados by Monday morning. Regardless of development increase in showers expected for the region. Beyond that is pretty much anyone’s guess. The subtropical ridge is well established across the subtropical Atlantic but there is weakness on its western end that may help ease the disturbance more towards the WNW, then NW in the Caribbean Sea. Now I cannot guarantee we will have a tropical storm from this, so I think areas like Jamaica, the Caymans and Cuba should monitor the system since conditions are forecasted to be conducive for development.

We may have some type of subtropical development offshore the US east Coast by mid-week as the northern section of the wave at 65W, interacts with a frontal trough along the Eastern CONUS. Anything developing would have a better chance north of the Bahamas where upper winds are expected to be more favourable. In addition, anything forming would ridge up along the US East Coast under the influence of deep layer troughing. Regardless of development , moisture expected to spread across Puerto Rico and Hispaniola later today and on Monday, reaching Cuba and the Southern Bahamas by Tuesday and possibly, the Florida Peninsula by Wednesday.

I will continue to monitor these features over the week. I will post an update in the comment section later this morning as visible imagery and QuikSCAT become available.


El Nino and the Earth's Rotation; Watching the Eastern Atlantic

By: Weather456, 10:25 AM GMT on July 17, 2009

Using the Earth’s Rotation to Explain El Nino

There are many climatic factors we use to monitor the El Nino Southern Oscillation Index (ENSO) such as the Southern Oscillation Index (SOI), the Multivariate ENSO Index (MEI) and sea surface anomalies, but have you ever considered the Earth’s Rotation as an indicator of El Nino? Variations in the earth rotational speed have known be caused by El Nino and La Nina phases, and then in turn may provide answers to the cause of the oscillation.

Atmospheric Angular Momentum (AAM)

To explain how the Earth’s rotation is related to ENSO, we must first describe atmospheric angular momentum, which is simply, the degree to which the earth’s rotation is slowed or increased due to drags along the surface caused by atmospheric conditions such as pressure and wind systems. Changes in AAM have known to increase/shorten the length of day by fractions of a millisecond. Based on the conservation of angular momentum theory, increases in westerly winds, increases the speed of rotation of the earth and increases in easterly winds, decreases the speed of rotation. Two major climatic oscillations have known to have this effect on the Earth’s rotation –ENSO and the Madden Julian Oscillation (MJO), which increases the westerly/easterlies, and increases/slows the earth rotation, respectively.

El Nino

There are currently two theories that describe the relationship between El Nino and angular momentum of the Earth. First, a NASA funded research hypothesises that as the trades weaken during El Nino and the westerly winds increase near the equator, the stress causes the earth to speed up in accordance to the conservation of angular momentum. Thus, El Nino events are likely to cause an increase in the Earth’s Atmospheric Angular Momentum. The second theory suggests a reversal of events occur. As westerly winds or any other atmospheric system increases the earth’s speed of rotation, this in turns energizes the Equatorial Kelvin wave that moves west across the Pacific Ocean. As this wave moves towards the west, the trades weaken and thus initiate the onset of El Nino. Effectively one can say that ENSO is really driven by the trade winds over the ENSO regions and the trade winds and Kelvin Waves are driven by Atmospheric Angular Momentum.

Figure 1. Atmospheric Angular Momentum (m/sec) and El Nino region 3.4 index (C) anomalies (1958-2009)

Figure 1 shows the relationship between the ENSO Index at Nino region 3.4 (Central Equatorial Pacific) and the Atmospheric Angular Momentum (AAM). The blue line shows the sea surface temperature anomalies while the red line indicates the AAM anomaly. One can point out the major El Nino and La Nina events by solely looking at the AAM anomalies. El Nino years are synonymous with increases in the AAM and vice versa for La Nina years, confirming the relationship between the ENSO and the earth’s rotation.

Tropical Update

I continue to monitor a tropical wave southwest of the Cape Verde Islands that possesses the potential to become the season’s next depression. Currently, satellite imagery showed the wave producing increase but disorganize shower activity, as the environment is only marginal at this time. Satellite imagery, MIMIC-TPW analysis, vorticity charts and QuikSCAT continue to show mid-low level cyclonic rotation along the wave axis near 13N/33-34W. What I am looking for today is increase persistence and organization of cloud clusters that would warrant an invest.

This wave will likely continue to towards the west as it is embedded within deep easterly flow south of the subtropical ridge and should reach the Antilles by next Tuesday. Will it develop? Conditions are expected to become conducive for development with low vertical shear as the subtropical jet stream lifts north, progressively warmer waters and dispersing African dust. Thus, this wave has the potential to develop as it heads west. Surprisingly, given the forecasted conditions, none of the global models develops this wave. By next weekend, the remainder of the western Caribbean and southeast United States should continue to monitor the wave as it coincides with a trough split situation over the Gulf of Mexico and additional development may occur near the Bahamas. Regardless of development, along with the tropical wave 51W, an increase in deep layer moisture expected to move into the Antilles from Sunday through Wednesday. Generally, 1-3 inches expected with locally higher amounts on windward facing slopes.

There are no other areas of interest to speak of in the Atlantic.


Tropical Update

By: Weather456, 10:30 AM GMT on July 15, 2009

A very broad area of low pressure extends from the Central Atlantic to the West Coast of Africa with two tropical waves located at 40W and 22W, both south of 16N. Satellite imagery showed showers are limited along these feature and that is likely due to marginal sea surface temperatures and a layer of Saharan Dust to the north. It is likely these features will not develop in the near term, but QuikSCAT and total precipitable water loops continue to show deep layer rotation along these features. These very vigorous tropical waves have the potential to develop further west under more favourable conditions.

There are several global models, which develop these features. First, the CMC develops the central Atlantic wave at 40W and tracks it west-northwest, reaching tropical storm strength as it crosses the Windwards Islands on Sunday. The 00Z GFS has a more northerly solution and keeps the feature an open low most of the way from 40W, across the Leeward Islands and then nearing the Bahamas next week. This model has trended south of the 06Z run. The UKMET shows some development with the feature near the Cape Verdes as it tracks west. Last, the ECMWF merges the two lows and track them west then northwest, reaching the Bahamas next Wednesday, similar to the GFS.

Each model shows some level of westward component to the wave and I will go with a track between the CMC and GFS/ECMWF. The reason being, there is a very strong subtropical ridge across the Atlantic and it is strengthening and expected to continue to build. This is likely going to track any feature almost due west. The feature (s) may find some weakness on the western edge of the high due to a vigorous trough that is expected to dip over the Eastern United States next week. However, I was looking that very same trough and it barely tracks across the Eastern CONUS to allow much curvature of any feature before reaching atleast the Bahamas, hence the GFS/ECMWF solutions.

So basically, we have a broad area of low pressure in the Eastern Atlantic centred on a few tropical waves that is not expected to develop in the near term, but should be watch in the long-term as they near the islands weekend. Regardless of development, increase in shower activity is most likely expected for the islands later this weekend and early next week.

Closer to home, the GFS continues to support development of a low pressure along the tail end of a frontal boundary across the Northern Gulf of Mexico next Sunday. The model has some support from the CMC and ECMWF, which tracks a low pressure from the Northern Gulf into the Florida Panhandle across the Southeast United States. I will continue to monitor this area, but regardless of development, increase in moisture expected for the Northern Gulf Coast and Southeast United States this weekend into next week.


Chances of a depression higher

By: Weather456, 10:34 AM GMT on July 14, 2009

There has been little change to the broad area of low pressure in the Central Atlantic. Satellite imagery showed cloud tops have warmed overnight but with cyclonic turning evident along the axis near 35W. Conditions remain favourable for some development of this feature as it tracks west-northwest over the next five of days. This development may be limited by dry air north of the system. Beyond five days, the survival of the system becomes problematic if it enters the Caribbean Sea where strong upper winds would halt development. If it moves north of islands, it may stand some chance. Currently, most of the models (GFS, ECMWF and CMC) agree that the system will move more towards the north and graze the Leeward Islands. I would expect a weaker system to take a westerly track as oppose to a deeper system, so it mainly depends on well this feature develops. For now, until convection redevelops along this feature, development is not expected over the next 24 hrs.

There is another feature further east just offshore the Cape Verde islands that may probably stand a better chance. The reason being, the feature at 35W is moistening and destabilizing the environment ahead of the feature. Satellite imagery showed mid-level turning along the axis of this feature but QuikSCAT showed little, indicating much of it is in the mid-levels. Only the UKMET develops this feature.

These two features will be watched as they head west and while development is not guaranteed, it certainly increases the chances of a tropical depression later this week.

Closer to home, the models are trying to spin up a low-pressure area along an old frontal boundary offshore the United States East Coast or in the Northern Gulf of Mexico. The models are showing a weak low pressure developing along the tail end of a frontal boundary and shifting northeast either across the Southeast United States or into the Atlantic and out to sea. I will continue to monitor this area.


Tropical Update: Watching the Eastern Atlantic

By: Weather456, 10:24 AM GMT on July 13, 2009

Let us not get to excited, but we may have something promising to watch during this week. If you remember, that over the past week I have looking at the GFS in developing a feature in the central Atlantic. Though the model was alone, it was the most persistent. Now, it seems the model is playing out. The model is forecasting an area of low pressure to develop out of the monsoon trough in the central Atlantic, with the aid of a passing tropical wave that emerged off the coast yesterday. On the 00Z run, it shows a low-pressure area developing as early as today and moving off towards the west northwest. How true is this? Well,

This morning’s satellite imagery show a noticeable increase in shower activity along a broad area of low pressure in the Central Atlantic, and further analysis revealed the area sits under anticyclonic outflow aloft with convergence and divergence. QuikSCAT also revealed southwesterlies south of the area of convection, which indicates the monsoon trough rather than the ITCZ. The area sits below 10N, and the GFS thinks it will pull north. Something I had not notice before was that conditions appear favourable ahead of this feature for the next 5 days. By looking at these parameters, it seems development is possible. Still I am not too excited about it for several reasons and one being the lack of model consensus. The models, including the GFS have not being doing well this year so right now the GFS could be alone or bullish. I will continue to monitor this area for further signs of development, but for now given it’s latitude and lack of model support, there is little expected over the next 24 hrs.

Regardless of development, this feature seems to head west with a define signature along the way. It should be near 60W by weekend, whether at South America or the Leeward Islands is to be determined.

There are no other areas of interest in the Atlantic


Tropical Update; El Nino is here

By: Weather456, 12:04 PM GMT on July 12, 2009

Solid as a rock

There is a very deep layer anticyclone located over Northern Texas, with anticyclonic flow dominating much of the Southern United States. Water vapour imagery showed most of the moisture remains on the periphery of the high with drier conditions at the heart. This dry and hot weather pattern has been lingering for the past weeks with stations across the state reporting rainfall as low as 20% of average and temperatures 5F above average. No wonder they referred to it as the death ridge. The ridge is expected to linger over the area for atleast the next 4 days but shifting west between 5-7 days. Little moisture is also expected across the state for the next week which is not good news, since drought is exceptionally high across the state. The ridge is a normal feature of the subtropical summer as it moves north from the Eastern Pacific during June and early July. It is also a feature of the North American Monsoon Season.

Fast Moving Upper Low

The pressure gradient to the south of the ridge was producing upper winds as high of 70 knots over the Gulf of Mexico on Saturday. These fast upper winds quickly steered an upper low from the Yucatan Channel to the coast of West Mexico in just 9 hours. The distance between the Channel and coast is about 660 miles, which means the upper low was moving at about 73 mph!

Eastern Atlantic development

Most of the global models continue to hint that a tropical wave will emerge over the Eastern Atlantic during the next 24 hrs with little development. The GFS has been developing this feature for the past week now as it interacted with a low-pressure area within the ITCZ. The last model runs show little development, but a pretty strong wave heading west. The ECMWF even amplifies the surface reflection of the wave as it nears the islands in 5 days. Here, I will go with the model consensus since sea surface temperatures are only marginable at best in the Central Atlantic, dust is expected to accompany the wave and the wave appears much weaker than forecasted for now.

However, most models do drop wind shear low enough over the next 5 days but are uncertain beyond, therefore the wave will be monitored as it head west.

El Nino is here

Over the past month and several weeks, there has been numerous evidence that El Nino continues to develop across the Equatorial Pacific. The oceanic Nino index, which is the average off all four Nino regions average 0.2 for the period April-May-June, which is significant, considering the previous index for March-April-May was -0.1.

On 9 July 2009, NOAA announced the formal arrival of El Nino citing continued increase in sea surface temperatures in the equatorial Eastern and Central Pacific Ocean. Currently, much of the area from 100W to 140W remains atleast 1C above average. During El Nino, the easterly trades weaken and even begin to change component and this was evident over the past month. The Southern Oscillation Index (SOI) rose sharply over the past week or two, which is opposite to what we normally observed during El Nino. However, in their regular commentary on the El Niño-Southern Oscillation, the Australian Bureau of Meteorology (BOM) indicated that this was due to local-scale pressure changes at Darwin, and Tahiti and should fall once more as larger scale effects take hold.

El Nino is expected to continue into the fall and winter of 2009-2010, and if it continues to intensify at the current rate could imply we might see some of the classic effects than the two most recent El Nino events, 2006 and 2002. El Nino normally brings an increase chance of storminess and rainfall to Equatorial regions of Western South America; Central America, and the Southern United States from California to Florida. Conversely, El Niño brings drier weather to the Eastern Caribbean and extremely dry conditions to Australia, and Indo-Asia regions.
The presence of El Nino will likely not affect the peak of the hurricane season since it is currently developing but should bring an early end to the season like 2006, 2004, and 2002. This and other factors imply a concentration of tropical cyclone activity during August and September and we may get a situation where we have several tropical cyclones active at the same time.


Tropical Update

By: Weather456, 11:01 AM GMT on July 10, 2009

Southeast United States/Gulf of Mexico

A frontal boundary is draped across the Southwest North Atlantic into the Eastern Gulf of Mexico with scattered showers extending across the area from Western Cuba, across the Florida Peninsula and along the southeast coast. Shortwave infrared imagery showed cyclonic turning within a region of showers offshore Georgia, which is probably the low pressure that was forecasted to move offshore the Southeast Coast. Expect this low to shift off towards northeast over the next 24 hrs. I will continue to monitor this feature but it is unlikely it will transition to anything subtropical. Expect a decrease in shower activity for the Southeast United States as the front clears the region and high pressure returns. Don’t rule out lingering moisture or the chance for afternoon thunderstorms.


Water vapour imagery showed large cyclonic flow across the Caribbean with its axis along 79W and an upper low along the axis just west of Jamaica near 18N. Very dry air is enveloped within the upper low leaving much of the Western Caribbean Sea dry, which includes the Caymans. However, the upper low will seek to enhance showers along its periphery later today across Jamaica, Cuba, Haiti, Central America and the Yucatan. Daytime heating and a passing tropical wave in the Eastern Caribbean will add into the mix.

Satellite imagery along with total precipitable water loop showed a tropical wave is entering the Eastern Caribbean along 61W south of 19N. This wave is displaying classic inverted V cloud patterns in clusters of heavy thunderstorms along the ITCZ near 9N. The wave is also generating scattered showers across the Southern Antilles and Trinidad and will continue to do so later today. Little moisture is expected further north across the Northeast Caribbean. As the wave moves into the Caribbean, it will continue to enhance the easterly trades behind it leading to some pretty gusty winds across the Windwards. Expect this tropical wave to continue west reaching south of Hispaniola by Saturday morning.

Tropical Atlantic

A typical tradewind inversion pattern is in place across the tropical Atlantic with patches of stratiform clouds embedded within the tradewind flow below a very dry mid-upper level airmass.

The tropical Atlantic though seemingly quiet for now, may get exciting early next week. The 00Z UKMET, GFS and ECMWF is hinting that a strong tropical wave will emerge over the Eastern Atlantic on Sunday/Monday and develop along the monsoon trough over the course of next week as it moves off towards the west. The GFS is the most aggressive, bringing the system to tropical storm strength. Most of the other reliable models think shear will be low enough to support cyclogenesis but sea surface temperatures remain marginal at best. I do believe a strong tropical will emerge but development remains uncertain at this time. I would like to see more model consensus in developing the wave also.


Tropical wave being monitored

Recurving Vs Landfalling Cape Verde Hurricanes

By: Weather456, 10:33 AM GMT on July 09, 2009

One of the most provocative questions that we ask every hurricane season would be what are the chances of Cape Verde Hurricanes (CVHs) affecting land areas in the Western Hemisphere. This question is often related to the East Coast of the United States but areas such as the Bahamas, Turks, and Northern Caribbean also is affected by whether a tropical cyclone re-curves or not. A recurving tropical cyclone is one that changes from a westerly to easterly component during the course of its life. The North Atlantic Oscillation (NAO) is probably the main factor in determining the mean longitude of recurvature (MLOR) each year.

The North Atlantic Oscillation

The North Atlantic Oscillation describes the difference between atmospheric pressures near the Icelandic Low near 60N and the Azores High near 30N. A negative NAO shows a weaker Icelandic Low and Azores High, while in the positive, a stronger/deeper of the two features occur. Over the past 58 years, patterns in the North Atlantic Oscillation provided forecasters with some level of accuracy in predicting landfalling CVHs. Probably the largest connection occurred between the NAO indices the December before the hurricane season as in Table 1.

Table 1. Unfavourable and Favorable steering patterns during the 8 recent hurricane seasons.

Table 1 shows the last eight hurricane seasons, the NAO oscillation the fall before, the recurvature pattern and notable Cape Verde Hurricanes during August, September and October, the peak of the Cape Verde Season (CVS). Years with negative NAO indices the fall before favour the landfall of CVHs the next hurricane season. The Hurricane Season of 2005, the most active on record, had 1 CVH during the peak of the season and it recurved out to sea. Conversely, other less active seasons with also 1 CVH, like 2008 and 2007 was very unfavourable. The 2002 hurricane season was relatively inactive and even below normal by ACE standards, yet the only CVH made it to the Gulf coast. The 2001 CVS was relatively more active (well above average) but both CVHs that year recurved out to sea.

Figure 1. Observed tracks of Cape Verde-type hurricanes in both phases of the NAO during the December before the hurricane season.

What Causes the NAO to have such an influence on hurricane tracks?

It is the two components of the oscillation, the Azores High and Icelandic Low, that act together to produce such variability in CVH tracks. The NAO phase the fall before normally reverses during the winter and spring (January-May) and returns again for summer and fall (June-December) which implies the NAO phase the previous fall normally indicates the NAO phase the next September.

In a negative NAO, the high is weaker but more sprawling and centralised, bridging further west along the US East Coast. The Icelandic Low is normally located over Eastern Canada/Davis Strait during summer and is a major component of mid-latitude (frontal) weather. During a negative NAO, the low is weaker than normally, indicating, weaker than normal mid-latitude weather and frontal troughs especially along the US East Coast. Therefore, we have a ridge extending further west and weaker troughs along the US East Coast, allowing the mean longitude of recurvature of CVH to be near 83.4W during negative events of the NAO.

In a positive NAO, roughly the opposite occurs, but the stronger than normally high is more developed in the North East Atlantic and does not bridge as far west as normal. You also have a deeper Icelandic Low, and more frontal activity, which in turn creates a favourable pattern. The mean longitude of recurvature during positive phases of the NAO is 61.5W.

Figure 2. 500 mb height anomalies for the month of September. Credit Australian Bureau of Meteorology (BOM)

Figure 2 shows the 500 mb height anomalies for the Western Hemisphere for two years, 2004 and 2006, which were oppositely, unfavourable and favourable years. If one was to direct their attention at the area from Eastern Canada to Greenland, one would notice the big difference in height anomalies. Higher than normal heights indicated a weaker Icelandic Low (2004), while lower than normal heights indicated a deeper Icelandic Low (2006). Similar results were produce in 2008 and 2007. The source of the data presented in this figure came from the BOM, which only goes back to 2002, but similar results were produce for 1998 and 2001. I was unable to provide an image since NOAA/ESRL website went down for maintenance during the construction of this report.

Other Years

Data on the NAO go back to about 58 years and there are still some inconsistencies in this correlation due to smaller scale modulators of steering flow. An example would be 1992, which showed a positive phase the fall before, but a landfalling CVH, Andrew. In addition, there is only an average 1 Cape Verde Storm a year, accounting for a smaller percentage of all destructive hurricanes.

However, the inconsistencies though seemingly important, are relatively small. Other accurate correlations were the negative phase of the NAO the fall before 1989 (Hugo) and 1998 (Georges), two storms that affected my area.

2009 Forecast

Last fall the NAO was in negative phase, which is probably what we might see this season, since the pattern over the last several weeks, and the forecasts issued by the Climate Forecast System (CFS) indicate we may be entering a negative phase of the NAO. Now we can look at all the troughs leaving the Eastern United States now, but that the CVS starts next month and peaks September. This really implies a greater risk for the Western Hemisphere this year regardless of storm numbers. Another problem 2009 poses is that tropical waves may not start to develop until about 50-60W, closer to home.

Decadal Influences

The 2000-2009 decade will go down as the most destructive decade in hurricane history. The human impact from Hurricanes Katrina, Ike, Wilma, Charley, Ivan, Rita and Frances, within the top 10, easily tops 150 billion US Dollars. The most notable storm in that list was Hurricane Ike, which was a Cape Verde Hurricane in 2008, and third costliest Hurricane, only behind Andrew and Katrina.

Figure 3. Average indices for July, August, September and October from 1990 to the present. Credit: NOAA/ESRL

Figure 3 shows the combinations of above normal sea surface temperatures contributed the ongoing Atlantic Multidecadal Oscillation (AMO) and persistent Negative NAO phases contributed to the increase intensity and frequency of landfalling hurricanes this decade. In an article from USA today, Dr. William Gray quoted that: “The NAO has been weaker than normal since 1995, and we've had more intense hurricanes during that period.”

Additional Information

North Atlantic Oscillation Realtime Products
Recurvature and landfall of hurricanes and their relationship to the North Atlantic Oscillation

Tropical Update

The tropics remain quiet this morning, with little to speak of. Most of the models develop an area of low pressure offshore the Southeast United States later tonight/early Friday but it is likely this feature will be non-tropical in nature. However, it will still be monitored for signs of subtropical development. Most of long-range models (MCM, EMCWF and GFS) show a low-pressure area in the Eastern Atlantic sometime next week. The GFS model has been forecasting the development of this feature for the past week and is the most aggressive of the three models. The source of development appears to stem from a vigorous monsoon trough, probably enhanced by a passing tropical wave. If the models continue to forecast development by Monday, the East Atlantic will be watched. Sea surface temperatures have significantly increased in the Tropical Atlantic and it seems models decrease shear enough during that time frame.


Solar System's Wild Weather

By: Weather456, 11:42 AM GMT on July 08, 2009

Extraterrestrial Weather

The next time you complain that it is 100 degrees outside or it’s frigid cold, try living elsewhere in the solar system where weather conditions become unimaginably extreme. Today I am going to look at how weather can get bad in the solar system from runaway global warming to a planetary dust storm.

Venus: Runaway Global Warming

One of the main causes of global warming is the build up of gases within the atmosphere that trap heat and cause the planet to warm, in a process called the greenhouse effect. One of the more common greenhouse gases is carbon dioxide and water vapour. Now, Venus’ atmosphere is extremely dense, about 100 times as dense as Earth’s atmosphere and contains 98% carbon dioxide. This C02 rich atmosphere along with thick sulphur dioxide clouds generates the strongest greenhouse effect in the Solar System. Temperatures on the Cytherean surface can reach 860F or 427C, hot enough to melt led! To bring this into perspective, temperatures on Mercury while it faces the sun reach 660F-860F or 348C-427C, which is nearly twice the distance nearer to the sun than Venus.

Scientists believe that Venus once retained liquid water on its surface but due a “runaway” greenhouse effect, most of it evaporated. Venus is also described as isothermal, in that, temperatures does not change significantly between day and night and from the equator to the poles. This is mind boggling since a day on Venus is longer than its year. The night side is prevented from cooling due to the transfer of heat from the dayside by winds. This is similar to the warming effect the Gulf Stream has the Atlantic coast of Europe.

Figure 1. Ultraviolet image of Venus' clouds as seen by the Pioneer Venus Orbiter (February 26, 1979). Notice, the thick sulphur dioxide clouds that blanket the whole planet.

Fugire 2. An artist interpretation of a volcano on Venus, adding to the hellish environment. As you may know, Earth's volcanoes are one of the features that expel carbon dioxide and water vapor into the atmosphere, two common greenhouse gases.

Mars: Dastardly Dust

Mars is a planet of very little moisture so dust and sand are always blowing. The planet is virtually the Saharan Desert on a planetary scale. Every few years, Mars is plague with large-scale dust storms that can cover the entire planet and block out the sun for several weeks. The dust on Mars is so prevalent that it gives the atmosphere a tawny colour when seen from the surface, which is the equivalent of the milky appearance the Saharan dust gives us here on Earth.

Another major component of the dust, is what we call dust devils, but these dust devils are comparable to tornadoes here on Earth. A Martian vortex can tower up 8000 meters compared to 610 meters into Earth’s atmosphere. These dust devils formed when hot air near the surface rises into pockets of cooler air, is stretched, and begins to rotate. Martian dust devils and windstorms have occasionally cleaned both rovers' (Spirit and Opportunity) solar panels, and thus increased their lifespan.

Figure 3. The artist seems to have intuitively included a glow discharge near the base of the dust devil. Credit: University of Michigan.

Figure 4. Dust devil on Mars, photographed by the Mars rover Spirit. The counter in the bottom-left corner indicates time in seconds after the first photo was taken in the sequence. At the final frames, one can see that the dust devil has left a trail on the Martian surface. Three other dust devils also appear in the background.

Jupiter: 300-Year-Old 'Hypercane'

Jupiter's Great Red Spot is the mother of all storms. This is the largest known storm in the solar system and has been raging for centuries. The storm is literally bigger than Earth itself. It's a whopping 15,400 miles (24,800 kilometres) across at its widest point. Moreover, it will not die.

The storm rotates counter-clockwise at 22 degrees south of Jupiter’s equator. Voyager flybys indicate that winds around the edge of the storm peak around 120 m/s or 265 mph. What really sets the storm apart from terrestrial cyclones is that the center is describe as stagnant, with little inflow or outflow and it is a high-pressured system (hard to believe).

The longevity of the storm can be tied to the fact that there are no solid surfaces on the face of Jupiter and thus nothing to slow down the storm like storms here on Earth. I believe the formation of the Great Red Spot may have been contributed by Kelvin–Helmholtz instability.

Figure 5. Paintlike swirls surround the Great Red Spot, a high-pressure area on Jupiter. Credit: NASA

Figure 6. Jupiter's Sea - deep beneath Jupiter's clouds, an exotic ocean of liquid hydrogen roils mysteriously.

Io – Volcanic Moon

During Voyager 1's fly-by of Jupiter in 1979, scientists expected to see numerous impact craters, like the one seen on the unchanged surfaces of the Moon, Mars and Mercury. However, they were surprised to discover that the surface was almost completely lacking in impact craters, but was instead covered in smooth plains dotted with tall mountains, pits of various shapes and sizes, and volcanic lava flows. Compared to most worlds observed to that point, Io's surface was covered in a variety of colourful materials (leading Io to be compared to a rotten orange or to pizza) from various sulphurous compounds.

The lack of impact craters indicated that Io's surface is geologically young, like the terrestrial surface; volcanic materials continuously bury craters as they are produced. This result was spectacularly confirmed as Voyager 1 observed at least nine active volcanoes. In addition, volcanic plumes were also observed extending several hundred kilometres above Io’s surface.

Figure 7. Sequence of five images taken by NASA's New Horizons probe on March 1st 2007, over the course of eight minutes from 23:50 UT. The images form an animation of an eruption by the Tvashtar Paterae volcanic region on the innermost of Jupiter's Galilean moons, Io. The plume is 330 km high, though only its uppermost half is visible in this image, as its source lies over the moon's limb on its far side.

Figure 8. What it might look if one was standing on Io viewing one of its volcanoes. That's Jupiter in the background filling the sky.

Pluto: Eternal Ice Age

Pluto is the most distance of the main planets, atleast until 2006, and thus makes it one of the coldest objects in the Solar System. In 1989, Pluto experienced its first day of summer (June 21 here on Earth) which lasts about 60 years. As a result, the temperature on the surface is a relatively pleasant -350F (-212C) these days and forecast to get colder.

Scientists think that during these glorious days of summer, Pluto "launders" its surface by evaporating old, dirty ice. When winter arrives, a fresh layer of ice will be deposited. But not all areas of Pluto are so warm today. Some regions, where the ice is thick, may be minus 380 degrees F (minus 228 degrees C).

Okay, fine. It's utterly frigid. At least there's no wind.


You might be thinking that Pluto has no atmosphere, but scientists say it does have just enough gravity to retain a little nitrogen gas, not to mention smaller amounts of carbon monoxide and methane. Moreover, the pressure gulf resulting from the tremendous temperature difference is thought to create high winds in Pluto's tenuous atmosphere.

Even Amundsen would turn back.

Figure 9. What it might look standing on Pluto viewing Charon, Pluto's companion (left) and the distance Sun (right).


Planet Earth is unique and as wild as weather can get here, it still allows an inhabitable environment for complex organisms due to oceanic and atmospheric regulators, which does not allow our planet to become too warm, too dry and too cold. If Earth was disappear now, we would not survive anywhere else in the solar system as we just saw how wild weather could get. It really brings to light how important weather shaped the evolution of life here. Therefore, the next time you feel like cursing the heck out of weather, pause to think how lucky we are, to be the third rock from the sun. and Wikipedia provided much of the information presented here and you can visit the websites for more interesting facts and information.

El Nino 2009

There have been numerous evidence that El Nino continues to establish itself across the Equatorial Pacific and it should not take long until NOAA issues an El Nino warning. On Sunday, if the tropics remain quiet, I will discuss some of the indicators of this year’s El Nino and comparisons to the 2006, 2002 and 1997 events. The atmospheric component of ENSO is not readily in place based on TRMM’s ENSO Precipitation Index (ESPI) which remains negative (cold phase of ENSO) and the rise in the Southern Oscillation Index (SOI) over the past weeks.


Tropical Update

By: Weather456, 10:46 AM GMT on July 07, 2009


The Atlantic tropics remain relatively quiet but we still have a few areas of interest out there. First, we have a low-level trough across the Western Caribbean that continues to interact with a very weak upper low to produce disorganize showers across Central America, the Caymans, Jamaica and Southeast Cuba. Expect this trough to continue to enhance showers across the area later today and as it moves over the Yucatan on Wednesday.

Meanwhile, a tropical wave is located in the Central Caribbean at 79W south of 18N. The northern part of the wave is expected to aid in additional showers over the aforementioned areas above later today but much of the wave is bound for Central America on Wednesday. This wave interacted with the TUTT over the past 2 days to produce heavy rains across Hispaniola. Some places in the Dominican Republic picked up amounts of 110 mm or 4 inches over the past 24 hrs.

I do not expect any development from these features but regardless, showers and isolated thunderstorms will spread across the area. Expect up to 1 inch of rain with local amounts up to 2 inches.

Dry then Wet, Dry Again

Upper confluent flow between two ridges in the tropical and subtropical Atlantic will maintain a dry airmass across the Eastern Caribbean later today. Expect little in the way of moisture. However, the southern Antilles may get a thundershower or two from the ITCZ, like northeast South America and Trinidad. Ironically, the large scale pattern remains dry across the Northeast Caribbean, but we just had a local scale thundershower here in Saint Kitts.

Model Consensus at Its Finest

There is no doubt that an area of low pressure will develop along a stationary front offshore the US east coast by Wednesday evening as every model indicates this. It is unlikely that the area will have enough time to become something subtropical as it moves off towards the northeast but worth watching since it is expected to traverse the Gulf Stream. Only a few models transition the system to a non-frontal feature but all agree it would end up as a non-tropical feature by weekend. Currently, there is some convective activity offshore but that is due to a frontal boundary.

East Atlantic Wave

This morning satellite imagery along with numerical models showed a highly amplified tropical wave in the Eastern Atlantic near 32W south of 15N moving off towards the west. Mid-level turning is evident along the axis near 11N with scattered showers within and around the axis. This is one the more vigorous waves that is able to maintain convection along the axis as it traverse the Atlantic. This is likely due to dust being well to the north and west of the system and moving over SSTs near 26C, which become progressively warmer. None of the models develops the wave but keeps its signature as it moves off towards the west. I will continue to monitor this feature over the next couple of days.


If you blinked, you would of missed Tropical Invest 94L, which was designated on Saturday but only lasted about 24 hrs due to high vertical shear. The system is now moving south of the Azores as forecasted and will affect the southern coasts with heavy wind and wave.

Forecasted Strong Wave

Most models indicate a strong tropical wave will emerge off the coast on Sunday and until that happens, if it happens, I cannot speculate on development and track.

My next blog will be on Wednesday and will discuss extraterrestrial weather if there is nothing significant in the tropics.


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Caribbean Coral Reefs and Climate Change

By: Weather456, 12:16 PM GMT on July 05, 2009

Coral reefs are the most diverse and beautiful of all marine habitats. There are comprised of aragonite structures produced by living organisms, found in marine waters containing few nutrients. In most reefs, the predominant organisms are stony corals, colonial cnidarians that secrete an exoskeleton of calcium carbonate. The accumulation of skeletal material, broken and piled up by wave action and bio-eroders, produces a calcareous formation that supports the living corals and a great variety of other animal and plant life.

Coral Reef Decline across the Caribbean

Over the past 3-4 decades, Caribbean coral reefs have been under threat from a number of causes including overfishing, coral mining, increase in sea surface temperatures (coral bleaching), hurricanes and oceanic acidification. In July 2003, a team of United Kingdom scientist compiled data from 263 separate reefs across the region and found that Caribbean reefs were down by 80%! They cited that human impact rather than global warming contributed to this decline between 1975 and 2000. However, this report was done before the record breaking 2005 Hurricane Season, when record high sea surface temperatures and intense hurricanes devastated more than half of Caribbean coral reefs. Other studies like the one did by Hoegh-Guldberg, O. et al. 2007 indicate that human-induced climate change is one of the main and undeniable threats. Climate change is having negative effects on coral populations via at least three mechanisms and this report seeks to address those factors.

Figure 1: Losses of live coral cover on Caribbean reefs since 1977. (Modified from Gardner et al. 2003; Photos by I.M. Côté)

Rising Ocean Temperatures

Continuing increase in greenhouse gases trap heat and lead to global warming. Increase in ocean temperature has been described as variable and subtle, increasing about 1C over the past decades. However, such modest increase in ocean temperature is still very noticeable during the summers, especially over the past 10 years.

The corals that form the structure of the great reef ecosystems of tropical seas depend on a symbiotic relationship with photosynthesizing unicellular algae called zooxanthellae that live within their tissues. The alga provides corals with food and oxygen while the corals in turn provide carbon dioxide, food and shelter for the algae. Pigmentation within the algae also gives coral reefs their unique colours and coral bleaching occurs when there is an expulsion of these algae due to an increase in sea surface temperatures, changes in water chemistry, pollution and diseases, which ultimately lead to the coral’s death.

Sea surface temperatures have been found to be the number one cause of coral bleaching during the summer and this was most evident during the winter of 1998, due to the 1997-98 El Nino and the summer of 2005, the warmest year on record.

Figure 2: Observed and forecasted increase in sea surface temperature for three locations worldwide. (Source: Hoegh-Guldberg 1999[4])

Figure 3: Coral bleaching Hotspots from August 27, 2005. Yellow to orange colours indicate areas above the bleaching threshold. Note the warm waters around the entire Caribbean region. (Source: NOAA)

Increase in Hurricane Activity

During the last decade, Atlantic hurricane activity has been in an upswing and this has led to an increase in intense hurricanes, in not only the tropical Atlantic, but also the Gulf of Mexico, Caribbean and Southwest North Atlantic, where most of the coral reefs are found. Large battering waves from hurricanes have significantly flattened corals and reduced their complexity. The 2005 hurricane season again proved to be a double whammy for Caribbean reefs where high ocean temperature contributed to increase coral bleaching and in turn fuelled intense hurricanes.

Oceanic Acidity

In the natural carbon cycle, the atmospheric concentration of carbon dioxide (CO2) represents a balance of fluxes between the oceans, terrestrial biosphere, lithosphere and the atmosphere. Since the 1700s, there has been numerous evidence that human activity have contributed to an increase level of carbon dioxide in the atmosphere. A combination of fossil fuel combustion and deforestation are two main reasons for the rise in C02 levels.

Now when C02 dissolves in oceanic water it reacts to form a carbonic acid (H2CO3). Dissolving CO2 in seawater also increases the hydrogen ion (H+) concentration in the ocean, and thus decreases ocean pH. The processes are a bit more complicated than this but results in a decrease of oceanic pH or acidification. Absorption of carbon dioxide in rainwater, which causes what is known as acid rain, also increases the acidity of the ocean.

As oceanic pH rises, structures made of calcium carbonate (corals) are vulnerable to dissolution. Research has already found that corals experience reduced calcification or enhanced dissolution when exposed to elevated CO2. In addition, corals become under stress when there is a change in the ocean’s chemistry, which can lead to coral bleaching.

Figure 4: Linkages between the build-up of atmospheric CO2, the acidification of the ocean and the slowing of coral calcification. (Source: Hoegh-Guldberg et al. 2007[2])

Figure 5: Changes in surface oceanic concentration of CO2 (left, in micro-atmospheres), and pH (right) from three locations. Blue is at 29°N, 15°W in the Canary Islands; green is at 23°N, 158°W in the Hawaiian Islands, and red is 31°N, 64°W at Bermuda. The mean seasonal cycle was removed from the data, and the thick black line is smoothed to not include any information less than 1/2 year in period. Note that as CO2 has risen, the pH of the oceans has fallen as the waters become more acid. (Source: IPCC 2007: The Physical Basis for Climate Change)


Coral reefs are very important to the Caribbean as they provide a home for millions of marine species. Coral reefs have also been found to help buffer the coast from the direct impact of hurricanes, which ironically is what helps destroy them, but with the former increasing yearly, an imbalance is formed. In addition to ecology and coastal protection, the Caribbean depends economically on coral reefs through tourism and fisheries, providing about 20-30 million dollars in revenue across the region.

Now during the El Nino of 1998, mass coral bleaching caused a 20% decrease in snorkelling and glass bottom boat tourism in Zanzibar and Sri Lanka and about 1.5 million US dollars loss in tourism in the Philippines. If climate change continues to affect Caribbean reefs, these losses may eventually be felt across our region and the impact factor maybe much greater since most countries have now become tourism orientated. The fishing industry will also be hurt as in Jamaica, when they reported in May 2009 that reef loss led to a reduction in fish populations.

Sadly, research centers, such as the Center for Sponsored Coastal Ocean Research (CSCOR) in Puerto Rico can provide management of coral reefs in relation to direct human impact, but impacts due to climate change is another story that I think is beyond the organization.

Figure 6: GDP contributors, Bahamas, 2001 est.

Summary and Future

We have seen how much climate change can have an impact on coral reef population across the Caribbean and with climate change ongoing, it is looking grim for our beloved marine ecosystems. Since the last decade or so, Caribbean economies have diverted from manufacturing to tourism and a mass reduction of coral reefs could be detrimental to nations especially Belize, United States (Florida) and the Bahamas.

I am expected do some more research on the tropic during the off-season of 2009-2010, so expect another blog on this topic as to what we can do to protect the corals.

Sources and Further Reading:


Patterns of Caribbean Coral loss and Coral reefs and climate change by the Encyclopaedia of earth, 2008

Coral reefs, coral bleaching, and oceanic acidification by Wikipedia, the Free Encyclopaedia.

Acid Oceans by Weatherundergound, 2008

Numerous internet articles by CNN, BBC, the Telegraph, 2002-present


Coral reefs By Marea Eleni Hatziolos, Anthony J. Hooten, Martin Fodor, World Bank, International Center for Living Aquatic Resources Management, 1998

A guide to the coral reefs of the Caribbean By Mark Spalding, Gillian Bunting, Corinna Ravilious, 2004

Tropical Update

Welcomed Rains

An upper trough north of Hispaniola interacting with a low-level trough across our region is generating scattered showers and thunderstorms across the Lesser Antilles, Puerto Rico and some is now reaching the Dominican Republic. Here in Saint Kitts, it’s been raining since about 2am this morning and my personal weather station here pick-up about ¾ inches. Not much but welcome rains in this period of continuing dry weather across the area. I took some pictures that are at the bottom of my blog so you can rate them. It seems we will have some more lingering moisture as a tropical enters the region today and provide some low level lift in conjunction with the upper trough over the Southwest North Atlantic.

Changes Are Coming

Most models indicate that a strong tropical wave will emerge off the coast of Africa around 12 July but development of this feature is uncertain since it lies at the end of most model cycles. The long-range GFS does develop this feature though around 19-21 July. Now the models were right about the last strong wave and that is the one that was enveloped within the African dust and had the nice mid-level spin last week. With the MJO expected to return during this period and vertical wind shear expected be low across the entire western Tropical Atlantic to Caribbean/Gulf of Mexico, this one will be watch when it happens, almost 2 weeks from now. Just a reminder that changes are coming.


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Tropics Relatively Quiet: Extratropical Invest 94L

By: Weather456, 12:39 PM GMT on July 04, 2009

A non-tropical area of low pressure is centered near 31N-38W moving off towards the east near 9 mph. Estimated surface winds have increased to near 40 knots and minimum central pressure is near 1012 millibars. The latest visible images continue to show the area remains under some westerly shear, but vertical shear maps from CIMSS showed significantly less than 24 hrs, resulting in a rather sheared but more organized system. QuikSCAT also revealed, the associated center of circulation remains well defined but with the maximum sustain winds some distance away from the center, a characteristic of subtropical cyclones.

The system is currently moving over waters near 25.5C, which is still warm enough for subtropical development and if vertical shear continues to decline then this system has a chance of becoming something subtropical before it becomes associated with a frontal boundary in 3-4 days. However, this time frame continues to become implicated by the slow motion of this feature.

Regardless of development, high wind and heavy surf may affect the Azores over the next couple of days, especially the southern facing shores.

Elsewhere, none of the models is indicating tropical development for atleast the next 3 days. However, I am monitoring the wave near 50W because even though it is enveloped within African dust it continues to possess define mid-level turning , so it could be watch as it enters of the Caribbean over the next 2-3 days. Also, the GFS is indicating some low pressure area may develop at the tail end of a frontal boundary offshore the Eastern United States next week but move off towards the northeast away from land. Otherwise, the deep tropics seem to remain quiet next week.


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Tropical Update

By: Weather456, 10:32 AM GMT on July 03, 2009

A non-tropical but non-frontal area of low pressure is located near 32N-45W moving slowly off towards the east. Estimated surface winds are near 25-30 knots with a minimum central pressure of 1014 millibars. Short-wave imagery this morning showed a very tight circulation associated with this feature and a QuikSCAT pass from this morning supported the finding with the highest winds found near the center. Satellite imagery also showed that the system remains under high wind shear with much of the convection well towards the east. Thus, development is not imminent. I did some subtropical analysis and shear patterns revealed an intensity of ST 1.5.

The only thing preventing this system from becoming subtropical is the warm-core element, which can only be acquired if the system is able to get convection near its center of circulation. 24hr Wind shear tendencies showed shear has decrease somewhat along this feature but remains around 25 knots and not forecast to drop. The area still stands a chance since it is moving over waters near 25C, well above the requirement for subtropical storms. It is expected to become associated with a frontal boundary as it continues east over the next 3 days.

Upper Low

An upper low/TUTT continues to make its way west northwest across Caribbean now situated in the NW Caribbean. The upper low continues to enhance showers and thunderstorms across Central America, Cuba, the Caymans and Northwest Caribbean waters. Expect the upper low to linger across the area while weakening and enhancing shower activity especially aiding in the development of afternoon thunderstorms.

Wave Train

There are a few tropical waves out in the Atlantic this morning with the first one along 88W south of 15N moving off towards the west near 10-15 knots. This wave is helping to enhance convection along the ITCZ across Panama and Colombia. The second wave is nearing the islands along 57W south of 15N with an increase in shower activity within 200 nmi either side of the wave axis, which includes Barbados, the Southern Windwards and Trinidad. The third wave is in the Central Atlantic near 35-40W south of 20N. The only convection along this wave appears in the ITCZ as much of the axis remains enveloped within a layer of African dust. A fourth wave is suspected to have emerged over the East Atlantic with little associated showers.

None of the models develops any of these features and for good reason. There is a good amount dry air extending from the tropical Atlantic into the Caribbean, but the main reason remains a band of heavy shear that is expected to persist from 80W to 45W south of 20N for atleast the next 4-5 days. These unfavorable factors will make it difficult for development to occur.

Elsewhere, there seems to be no threat of tropical development over the weekend. Have a great independence weekend, both Americans on the mainland and those living overseas especially here in the Caribbean.


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Looking At African Dust

By: Weather456, 11:02 AM GMT on July 02, 2009

This morning Saharan Air Analysis (SAL) analysis maps at the CIMSS revealed a large area of African Dust stretching over the Eastern Atlantic. The dust is so intense that it can be notice on infrared imagery, roughly at the temperature of stratus clouds, indicating there is some radiative cooling at the top of the SAL layer. This intriguing observation indicates three things:

1)Supports the idea that mid-level cooling within the SAL layer do hinder convection along tropical waves,

2)Prevents much of the incoming radiation from reaching the sea surface, thus cooling it, and

3)The thickness of the SAL layer

Enveloped African Wave

The SAL layer normally has an anticyclonic twist to it, but recent infrared imagery showed the layer moving off towards the west in a cyclonic fashion. The wave that moved off the coast with the SAL layer eventually was enveloped within the layer and now cyclonic curvature along the wave is now warping the entire mid-low level cloud field.

Aerosol Observations

Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are smoke, oceanic haze, air pollution, smog, dust and CS gas.

Aerosol optical thickness maps show the amount of radiation that is depleted as a beam passes through a layer of the atmosphere. NOAA-18 analysis in the map below revealed where the SAL layer was found on 1 July, as the area of relatively high optical thickness.


MODIS polar orbiting satellites also capture the region of African Dust as it emerged off the coast yesterday along with a tropical wave to its south. This revealed an ideal structure of the tropical Atmosphere across the Eastern Tropical Atlantic where we have dust to the north and the ITCZ, and tropical waves to the south.

Vertical Structure

There is a perception that the SAL layer extends through the atmosphere but that is not entirely true. The SAL layer extends from the boundary later upwards to about 600 mb. This is the main reason why the SAL layer is rarely seen on water vapour imagery, which shows the upper level vapour flow. A more ideal product would be the total precipitable water column which the amount of water within a column of the atmosphere if it all condense and precipitate.

Below, is an upper air cross section of Sal, Cape Verde Islands showing the SAL layer extended from the boundary layer (as it is suspended layer) to about 650 mb on 1 July.

Check out my blog on 31 May 2009, Understanding the Atlantic Hurricane Season: The Saharan Air Layer


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First Day of July

By: Weather456, 10:57 AM GMT on July 01, 2009

The tropics remain quiet this first day of July, which is typically normal for this time of year. I expected a near average season, so each month should be near the long-term mean, as June was. In my July outlook, I indicated that more than half of hurricane seasons see their first named storm by July 11 and the other by August, so we have a decent chance of seeing our first named storm this month. Let’s see what’s going on in the tropics this morning.

Moisture Plume

A very broad upper low sits over the Eastern Great Lakes with westerly cyclonic flow dominating its southern half. This flow is advecting numerous scattered cloudiness and showers in a band that stretches from Texas across the Southwest North Atlantic and into the Central Subtropical Atlantic near 45W. Meanwhile, a few surface troughs and a weak frontal boundary may occasionally enhance this moisture plume. Expect this moisture plume to linger and continue to enhance moisture across Florida and the Bahamas with a frontal boundary adding to the mix over the next 2-3 days.

Dancing Upper Low

A large upper low is centred just south of Jamaica near 17N-77W moving off towards the west. This upper low envelopes the entire upper atmosphere across the Caribbean and is helping to generate moisture mainly to its southwest and east, while funnelling dry air to its northwest over Cuba and the Caymans. This upper low should quickly move off towards the west-northwest, reaching the Yucatan Peninsula by Friday. This feature will probably continue to enhance showers and thunderstorms over Central America as it does so.

Atlantic Tropical Waves and Dust Intimacy

There are few tropical waves in the Atlantic that continues to be enveloped within a layer of African Dust that stretches from West Africa to the western tropical Atlantic. The first wave is entering the Eastern Caribbean, now along 59W and is helping to enhance some moisture across the Southern Antilles. Expect this wave to reach the Western Caribbean by Friday.

The second wave is almost at 40W south of 15N, moving off towards the west at five longitudes a day. The northern part of this wave remains embedded within the SAL, with cyclonic curvature within the mid-low level cloud field, while southern extension is enhancing numerous showers along the ITCZ. Expect this wave to continue slowly westward with little development expected in the near term.

The third wave just emerged off Africa and with it comes some intense dust, seen clearly on visible imagery.

Some of the models are showing development off the Southeast coast next week so I’ll be watching that area. However, the models are hinting the area maybe picked up and swiftly carried off towards the northeast.

I would be a member for 4 years on Weatherundergound this July.


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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.