Weather456's Tropical Weather Blog

September Outlook; Jimena; 94L

By: Weather456, 10:05 AM GMT on August 31, 2009

August Summary

Table 1. Tropical activity recorded for the month of August 2009.

August activity was along the long-term average but remained slightly less active than the 1995-2008 averaged. My August forecast called for a 70% chance of at least three named storms, with a likely chance of one of those becoming a hurricane. The month ended with four named storms, 1 that became a hurricane and a major hurricane. The forecast skill was very satisfactory for the month.

Vertical shear remained near or below average for most parts of the Atlantic basin except for the Caribbean Sea where upper winds remained more unfavourable than usual for a third straight month. Nothing developed in the Caribbean Sea for the month and the 1 system that entered the basin encountered dry and south-westerly upper shear east of the TUTT. This shear pattern was expected and the TUTT was near its forecasted position of 70W.

Sea surface temperature anomalies for the month remain near 0.5-1.0C above normal, with the greatest anomalies off the coast of Africa and across the Northern Gulf Stream. Continued warm ocean temperatures played a role in the quick development of Claudette and the rapid intensification of Bill to a category 4 hurricane.

Dust remained a major problem into the first two weeks of August but gradually lessen as we neared the mid-latter part of August. Even Bill at one point was affected by dust. The tropical Atlantic remained more stable than usual for the month of August. This however became less of a problem as we neared the peak of the hurricane season.

Also included in the August outlook was an overview of the steering pattern, which also verified. Persistent troughing along the United States East continued into August, which idealistically helped recurved Hurricane Bill and Tropical Storm Danny from a direct United States impact. Unfortunately, both systems including 98L of late July were all steered into the New England area thus if this pattern continues into September those folks will really have to be on guard.

I also stressed the fact that this trough sometimes break and does not protect everyone like the case with Claudette.

Figure 1. Tropical activity recorded for the month of August 2009.

September Outlook

The peak of the hurricane season occurs in September and corresponds to low wind shear and the warmest sea surface temperatures. The month of September sees an average of three storms a year. By September 24, the average season sees seven named systems, four of which are hurricanes. In addition, two major hurricanes occur on average by September 28. This season is progressing rather normally so I expect a 70% chance of 4-5 named storms during the month of September.

September is capable of producing some of the most destructive and memorable storms in history as far back as the Labour Day Hurricane. Other recent September storms include Hurricanes Hugo (1989), Georges (1998), Ivan (2004), Jeanne (2004), Rita (2005), Felix (2007) and Ike (2008).

Figure 2. Tracks of all September storms occuring between 1886 and 2006. Basically, this is when everywhere becomes favorable for TC development.

Vertical Wind Shear

Low vertical wind shear dominates the same areas as in August but the Caribbean may become a little more conducive. However, the main hot spots continue to be the Gulf of Mexico, Southwest Atlantic and the Tropical Atlantic. Shear in the Caribbean fluctuates but averages out 15 knots for the month, which is rather marginally when it comes to tropical cyclogenesis. I expect the majority of those storms to be Cape Verde type systems with the latter in the Gulf and along the United States East Coast.

Figure 3. 31-day moving-average vertical shear values ending 26 August 2009 showing the four locations where Ana (A), Bill (B), Claudette (C) and Danny (D) all reached their peak intensities within environments where shear was well below 10 m/s or 22 mph, the threshold for cyclogenesis. Notice shear remained above average in the Caribbean Sea where no tropical cyclones occurred during the month.

Figure 4. GFS 200-850 mb long-range shear forecast valid through 1200Z September 15 2009, around the peak of the hurricane season showing low shear values similar to August across the Tropical Atlantic and Gulf of Mexico, with marginal shear values hanging around the Caribbean due to the presence of the tropical upper tropospheric trough (TUTT).

Sea Surface Temperatures

Sea surface temperatures continue to rise through August but the anomalies themselves remain unchanged. In fact, Hurricane Bill cooled an extensive area of the North Atlantic and thus development maybe slowed in that region for the next 2 weeks. However, sea temperatures are very dynamic and just could easily warm back to normal levels. Bill reached peak intensity relatively north of the deep tropics so ocean heat content in the Main Development Region remains relatively untapped and has enough energy to support two additional major hurricanes.

Figure 5. Operational SST Anomaly Charts (C) for August 27 2009 from NOAA/NESDIS. Most of the Atlantic remains near normal or above normal especially off the coast of Africa but Hurricane Bill has cooled a significant part of the subtropical Atlantic.

The Madden Julian Oscillation (MJO)

After a rather upswing beat during the last 3 weeks of August, the MJO is returning to neutral for the next 3 weeks. This should not be confused with the downward motion of the MJO, which suppresses tropical cyclone activity all together, but rather it will not play a significant role in cyclogenesis hence the term neutral. Most of the long range and climate models are in agreement with this solution with an upward swing returning during the last week of September, which can often produce some significant systems, i.e. Hurricane Jeanne 2004.

Figure 6. Experimental forecast probability of a tropical cyclone including only the seasonal cycle and MJO patterns. This product is still experimental but values less that 0.1 were forecasted during June and July 2009 with values of 0.3 forecasted for August. Thus it fairly safe to say that September will be a bit more active than August under anomalous MJO patterns.

Steering Pattern

The steering forecast issued in August was valid through 25 September and it seems the trough-like pattern will continue to into September but it a bit further west than August. The GFS 500 mb forecast through 15 September shows an increase in 500 mb storm tracks over the Eastern United States and the North Atlantic, much more than June, July and August. In addition, the CFS climate model run through September 28 continues to show rainfall maximas along the United States East Coast indicating more frontal activity.

This set-up may “semi-protect” the East Coast during the month of September so folks should continue to monitor the tropics regardless. The same is true for the Caribbean, which was spared the wrath of Bill due to a weakness in the subtropical ridge. However, the New England and Canadian coasts may not be as lucky since the storms are being steering into their region. Non-tropical Invest 98L, Hurricane Bill and Ex-Danny all affected the Northeast portion of the United States and Canada.

Figure 7. Forecast of the location where the 500 mb pressure surface will be at a height of 582 decametres (5280 meters) above sea level based on the GFS 2 week forecast. 500 mb is the pressure level where both shortwave and longwave troughs are normally found. This pattern of “troughiness” along the United States East favours the continued recurvature of systems as we saw in July and August of this year.


The month of September normally sees an average of three named storms per year and given that this year is progressing at an average pace, I expect something along those lines. The major inhibiting factor will be Bill’s cool wake. As those sea surface temperatures re-warm, along with low vertical shear and a higher probability of tropical cyclogenesis than normal due to the MJO and other seasonal patterns, I am expecting a 70% chance of 4-5 named storms, 2-3 hurricanes and 1 additional major hurricane during the month of September.

Tropical Update

Hurricane Jimena rapidly intensified into a category 4 hurricane on Sunday and posses a major threat to the Baja Peninsula later this week. The hurricane was last located at 17.5N-107.9W or about 395 miles south of Cabo San Lucas, Mexico. The system is moving off towards the northwest near 8 mph with estimated wind speeds of 145 mph and a minimum central pressure of 940 mb.

Jimena should reach the Baja Peninsula around Tuesday night as a major hurricane, not likely as strong as it is now but a devastating hurricane nonetheless. The Mexican government have already issued many weather alerts for the southern portion of the state of Baja California including a hurricane watch, flood watches and high surf and debris warnings.

The track of Jimena will determine if the core of intense winds will affect the city of Cabo San Lucas, which is located on the southwest tip of Baja. The latest forecast advisory has Jimena track just to the west of the city in about 33-48 hrs with only category one force winds reaching the coast. The heaviest core remains offshore. However, the storm eventually makes landfall further north along the coast bringing those strong winds ashore. It is likely that Cabo will incur some damages including sporadic power outages.

Estimated rainfall from Jimena could reach 4-8 inches with higher local amounts. The area is semi-mountainous and thus some flooding and landslides are possible. Fortunately, the towns on the peninsula are remotely distributed so the chance of incurring significant wind and rain damage is slimmed, not slim.

Jimena is also generating a 10-14 ft swell that is travelling up the coast towards the Baja. Some locations along the Mexican west coast could experience relatively high surf. Storm surge is a threat with 5-10 ft water rise expected along the peninsula. Fortunately here, it is not like the Gulf of Mexico as the area not surrounded by a large continental shelf.

Nevertheless, Jimena will be bad for the state and maybe even worst for Cabo San Lucas. The last hurricane to impact the peninsula was Hurricane Norbert of last November.

Figure 8. Jimena predicted windfield in 48 hrs along the forecast track issued at 2am PDT or 5am EDT.

Tropical Invest 94L

Tropical Invest 94L is estimated to located near 14.3N-51W or 800 miles east-southeast of the Leeward Islands moving off towards the west-northwest to northwest near 10-15 mph. Estimated surface winds are 25 knots with a minimum central pressure of 1006 mb. Satellite imagery showed 94L again feeling the effects of diurnal convective maximum as it develops convection near the center of circulation during the early morning hours of Monday. There are also some impressive cloud bands surrounding the northern semicircle of the storm. Conditions remain favourable for development as the upper anticyclone over the system continues to buffer the storm and as I stated yesterday, the band of 80 knots of vertical shear is a product of the system’s anticyclone interacting with the string of upper pearls known as the TUTT. I expect at least a named storm from this system later this week but only after it is able to survive diurnal cycles.

One indication that the system has become better define is the models are now making sense. Most of statistical models are showing 94L moving over the Northern Leeward Islands in about 2 days while dynamic models place the system north of the islands, but it doesn’t seem to make a big difference. The dynamic models also slows the storm down dramatically as it now takes 3 days to reach the islands when the expected date was 48 hrs yesterday and this is likely due to a weakness. I expect 94L to continue off towards the west-northwest to northwest with some decrease in forward motion as the subtropical ridge is interrupted by a series of deep layer upper low cells. This motion should bring 94L close enough to the islands to affect their/our weather by mid-week.

Through days 4-5, the ridge apparently re-establishes itself and 94L seems to continue off towards the west-northwest in the general direction of Danny. The models have increasingly hinted this solution over the past 12 hrs or so. Interest in the Leeward Islands and Puerto Rico should continue to monitor the progress of 94L.

Figure 9. GOES-12 infrared image of Tropical Invest 94L.

Figure 10. Tropical iInvest 94L 0600Z model suits.


Lesser Antilles need to watch 94L

By: Weather456, 11:27 AM GMT on August 30, 2009

Tropical Invest 94L has shown some improvement after a brief encounter with a bit of easterly shear cooler sea surface temperatures. If you remember, I stated yesterday that there was still the chance it could regain organization as it enters progressively warmer waters, the upper level environment improves, and it seems to have taken advantage of that.

Tropical Invest 94L was estimated to be located near 11.5N-46.0W or 986 miles east-southeast of Barbados; moving off towards the west to west-northwest or 310 degrees at 10-15 mph. Estimated surface winds are near 30 mph with a minimum central pressure of 1009 mb. Satellite imagery showed an increase in the intensity and organization of 94L around a vigorous circulation area. QuikSCAT manage to catch half of the circulation this morning, revealing a somewhat define center of circulation with 20-30 knots winds. The system continues to move under the light upper winds of an upper anticyclone with 28C waters. There is band of very strong upper winds north of 94L and according to how the system tracks it maybe either detrimental or beneficial to the outflow of this system. I expect the system to continue to slowly organize over the next day or two as it heads west-northwest then northwest.

My thinking on track remains unchanged from yesterday. I am expecting 94L to continue to move west northwest over the next 48 hrs and then turn more towards the northwest through day 2-3 days as a weakness develops in the subtropical ridge. This weakness is best viewed on water vapour imagery near 65W where the flow slows down and changes direction. I do not expect 94L to quickly turn towards the northwest as some of the models have been stating since 2 days (which continues to be wrong). Thus, this northward turn should be gradual and may bring it very close to the Northern Islands, hence the southern model consensus and the ECMWF.

It is becoming more likely that this feature will affect the weather in the Leeward Islands and maybe even Puerto Rico later this week. Interest in the islands should monitor the progress of 94L as it may end up more than just a broad area of showers.

Long term speaking, after it leaves the islands (either over or to the north), some models show 94L continuing off towards the northwest, similar to Danny as the ridge rebuilds and a trough stalls across the East Coast. It is still rather difficult to say what 94L will do beyond 5 days.

Figure 1. Water vapor image depiction of the general flow and expected motion of 94L over the next several days.

Hurricane Jimena

Hurricane Jimena continues to intensify and is now up to major hurricane status. The Eastern Pacific is really showing what it is capable of during El Nino years. This storm is expected to remain a major hurricane as it heads north-northeast over the next 2 days which may bring it along the Baja Peninsula by mid-week. The outer rain bands have already been lashing the coastal areas of Western-central Mexico and rough surf is expected to affect some of the most popular coastal destinations. I will have more on Jimena on Monday.

Figure 2. Hurricane Jimena 5 day forecast track.


Ex-Danny maybe has gone but not before dumping heavy rains, bringing gusty winds and high surf to the Northeast yesterday. Radar estimates reached as high as 10 inches just south of Cape Cod and again across northeast Maine, New Brunswick and Nova Scotia. The highest observed rainfall ranged from 1.5 inches to 4 inches.

Table 1. Observed rainfall totals for several locations across the Northeast United States/Southeast Canada valid midnight 30 August 2009.

Figure 3. Radar estimates over the past 24 hrs for the Northeast United States/Southeastern Canada.


Both Danny Boy and Erika-wannabe loses steam; Katrina Video Tributes

By: Weather456, 12:45 PM GMT on August 29, 2009

Water vapour imagery clearly shows Danny has become elongated and is being absorbed by an upper level system moving over North Carolina. Danny is expected to become fully absorbed later today and move towards the northeast along the Northeastern Seaboard as a non-tropical storm. Just because Danny is no longer tropical does not mean its dead. The remnant of Danny is currently spreading heavy rain across the coastal Mid-Atlantic States. Along with heavy rains (3-5 inches), blustery winds and choppy seas/high surf of 18 ft over open waters and 6-10 ft along the coast.

Figure 1. Water vapor imagery of the upper level system absorbing Danny.

Figure 2. Visible imagery of the resultant system as Danny merges with the upper level system.

Figure 3. Webcam shot of Cape May, NJ, taken 8:29 AM EDT this morning.

Tropical Invest 94L is suspected to located near 10.0N-40.5W or mid-way between Africa and the Lesser Antilles, moving off towards the west near 10-15 mph. Estimated surface winds are near 30 mph with a central pressure of 1008 mb. Visible satellite imagery of 94L continues to reveal a relatively broad disturbance and this center was determined using a blend of QuikSCAT and curved band techniques derived from Dvorak classification. Showers have also become significantly less organized. The disturbance is moving under the very light upper winds of an upper anticyclone but over the past 24 hrs, it has been traversing 26C waters, likely the cause of its deterioration. There is still a chance that this system could regain organization today and on Sunday as it continues to enter significantly warmer waters of 28-29C.

The unexpected delay in development probably has skewed the forecast track. 94L is located near 10N at 40W, while Bill was located 2 ½ degrees more north at that time and was moving west-northwest as a tropical storm. I am expecting 94L to move off towards the west over the next day or two, and then turn towards the west-northwest around 45W, with a bit more northwestward motion through days 3-5. This motion should bring the system close to the Antilles in about 5-6 days. My reasoning is that, unless 94L becomes a significantly deep system over the next 5 days, it will be steered by shallow-mid level flow, which shows some significant ridging through 3 days, and then a more pronounce weakness thereafter.

The computer models have been split on track and since the northern half have not verified it is only better judgement to go with the southern consensus. Interest in the islands should continue to monitor the progress of 94L.

Figure 4. Tropical Invest 94L model guidance at 0600Z 29 August 2009.

Hurricane Katrina 4 years later

Here are several videos that I made in October 2005 of the effects of Katrina in South Florida and the Gulf Coast of the United States. As you may know, 4 years ago today, Hurricane Katrina, the most devastating storm in US History made landfall along the northern Gulf Coast, forever changing the face of New Orleans.

Katrina Part 1 - Florida

Katrina Parts 2 and 4 - Gulf Coast


Tropical Storm Danny weakens; Tropical Invest 94L continues to organize

By: Weather456, 10:09 AM GMT on August 28, 2009

Figure 1. Water vapor imagery showing an overview of the Tropical Atlantic. Also focus your attention the upper level system spinning along the northern Gulf Coast. That is apart of a shortwave trough that will help push Bill out to sea.

Tropical Storm Danny was located near 29.5N-74.4W or about 400 miles south of Cape Hatteras, North Carolina, moving off towards the north-northwest near 9 mph. Estimated surface winds have dropped to 40 mph, with a minimum central pressure of 1008 millibars. Satellite imagery indicates that a combination of 20 knots of upper winds and dry air intrusion is resulting in a deterioration of Danny’s overall structure. This is expected over the next 1-2 days, as there appears to be little change in the upper pattern but some re-strengthening is possible before Danny enters a baroclinic zone and becomes extratropical by Monday.

Over the past 24 hrs, Danny remained under the influence of a deep layer ridge off to his north and east. He has now turned more towards the north as the shortwave over the Southeastern United States continues to amplify and shift east. On this present path, Danny is expected to pass about 125 miles offshore the North Carolina Outerbanks over the next 24-36 hrs. Afterwhich, a more pronounce long-wave trough turns him north and then northeast through 48 hrs. By this time, Danny is expected to deepen to a significant system but probably as a non-tropical entity and impact the New England and Canadian coasts.

Much of Danny’s high winds remain in the northeast quadrant, which should remain offshore as he passes so currently, the biggest effects and concerns will be high surf, on the order of about 5-7 ft that will continue to impact the Southeast United States, producing dangerous rip currents. Some increase in wave and wind action maybe felt along the coast as Danny passes the Outerbanks later today and on Saturday. Moderate to strong gale force winds, seas of 12-15 ft and about 3-4 inches of rain are expected to affect the New England and Canadian coasts later this weekend into early next week.

Figure 2. Model guidance for Tropical Storm Danny as of 0600Z 28 August 2009.

Tropical Invest 94L

Tropical Invest 94L was located near 10.2N-32.0W or about 450 miles southwest of the Cape Verde Islands moving off towards the west near 10-15 mph. Estimated surface winds are near 30 mph, with a minimum central pressure of 1009 mb. Satellite imagery continue to show a fairly organize system but the first visible images reveal the center of circulation remains east of the deep convection due to easterly shear. QuikSCAT caught the system this morning, revealing a broad low-level closed circulation. Despite this, upper level winds are expected to slacken as the system moves away from the African Easterlies and the development of an upper anticyclone is expected to produce ideal upper level conditions for further organization. I expect Tropical Depression 6 to form before the weekend is over and there is a good chance that Tropical Storm Erika will form before the month is over.

Currently 94L is moving under the influence of the subtropical ridge to its north and thus a west to west-northwest motion is expected over the next several days. However, most of the model guidance is indicating that 94L will feel some weakness induce by the trough currently over the Eastern United States by the time it reaches the Central Atlantic. The big question is, whether the trough will grip 94L and take it out to sea or induce the northward motion but is too far north or weak and it resumes its westward motion, similar to Ike of last year. I will have more details on track as the feature develops.

Figure 3. Model guidance for 94L as of 0600Z 28 August 2009.


Tropical Storm Danny; New African Disturbance

By: Weather456, 10:30 AM GMT on August 27, 2009

Figure 1. This morning's infrared image of Tropical Storm Danny.

As of 5AM EDT, Tropical Storm Danny was located near 27.4N-72.1W or 370 miles east-northeast of Nassau, Bahamas. The storm is moving off towards the northwest near 10 mph; with sustain winds of 60mph and a central pressure of 1006 mb. Satellite and microwave imageries continue to show Danny remains a disorganize system and I’m surprise that the Hurricane Hunters were able to find winds of 60 mph. These winds however remain to the north and east of the center of circulation due to 20 knots of vertical wind shear. However, Danny could become a little stronger over the next 2-4 days as it continues to break ties with the upper low to its south which has cause some imporvement over the past few hours. Sea surface temperatures are very warm underneath Danny, which could easily support a hurricane under the right upper level conditions.

Figure 2. TRMM 85GHz shot of Danny this morning revealing a somewhat disorganize system.

Danny continues to move towards the northwest under the steering flow of a deep layer ridge to its northeast and this motion is expected through the next 24 hrs. As a shortwave trough amplifies and push east along the coast of the Southeast, this should induce a more north-northwesterly then northerly track through 48 hrs at which point the system is expected pass along the Outerbanks of North Carolina. Through 72-120 hrs, a more amplified long-wave trough turns the system more towards the east bringing the system close to New England and the Canadian Maritimes. This is the track I’m leaning towards at this time, as it has verified over the past 2 days.

Regardless of how close Danny comes to the East Coast of the United States, rough surf of 5-7 ft could produce dangerous rip tides along the coast. The biggest danger of Danny’s waves are that they are not as big as Bill’s wave so more persons are attracted and endanger themselves. If Danny decides to come closer than expected, then gusty winds, and heavy rains are possible along the Outerbanks, which could cause minor damage and/or flooding.

Cyclone phase diagrams indicate that Danny may become an extratropical entity before reaching Nova Scotia but the same effects of Bill probably a little worst will be felt along the New England and Canadian coasts. Danny is about 100 miles closer to the coast than Bill and expected to be a category 1 like Bill when it impacts those areas. Choppy seas, gusty winds and heavy rains can be expected.

New England Hurricane Season

Persistent troughing along the United States East Coast continues to drive disturbances up the coast and directly into the New England area. The first of such occurrence was Non-tropical Invest 98L which developed along a baroclinic zone northeast of the Bahamas and moved north bringing tropical storm conditions to the region. The second was Hurricane Bill, which brought gusty winds and very rough surf as it pass close to Cape Cod last weekend. Now we have Danny, which could potentially bring a combination of both to the region.

African Disturbance

An area of disturbed weather southwest of the Cape Verde Islands continue to produce organize convection and shows some signs of atmospheric turning. QuikSCAT this morning also revealed a partial look of the system, which may hint a surface circulation. This disturbance is moving under light upper winds with 28-29C waters so development is anticipated and this could become our next invest, 94L.

Currently some models have backed off the system but a west to west-northwest motion is expected over the next couple of days and the tricky part is, there are no weaknesses out to 7 days as with Bill so folks in the islands should watch this one.

More details as the feature develops.

Figure 3. Visible image of the disturbance southwest of the Cape Verde Islands in the Eastern Atlantic.


Tropical Invest 92L heads west-northwest

By: Weather456, 10:07 AM GMT on August 26, 2009

As of 0215 AST this morning, Tropical Invest 92L was located near 24.1N-67.8W moving off towards the west-northwest near 20 mph. Estimated surface winds are near 45mph with an estimated low pressure area of 1010 mb. Satellite imagery continues to show the interaction between a weakening upper low and a surface trough of low pressure to produce clusters of heavy thunderstorms. Shortwave infrared imagery along with surface observations indicates that a surface circulation maybe trying to form near the estimated position. It is unclear, until we get visible images, if one has form. Upper winds has dropped to about 10-20 knots over the disturbance as the upper low dilutes. I suspect as the feature moves away from the upper low, that the environment becomes a bit more favourable for development.

Estimated motion is about west-northwest, and this motion is expected to continue for the next 24 hrs with a little northwest motion through 48 hrs, placing the system northeast of the Bahamian Islands. Through 72 hrs, a shortwave trough currently located over the Southern United States is amplified and push east by a larger long-wave trough over the upper Mid-West. This trough should induce a more northerly component from day 3 to 5. Now the tricky part is how the current motion and set-up of the trough will affect the future track of the system. If the system continues on its present motion and the trough sets up further west, then the system could come close to the Bahamas and the Southeastern United States as oppose to the trough setting up further east, which would favour a more offshore track. Again here, I will use better judgement and go with a blend of the model consensus, water vapour flow and steering maps, which may bring it a bit more closer to the Bahamas and Outerbanks of North Carolina.

Regardless of development, gusty winds and choppy seas may impact the Bahamas and Florida as the pressure gradient between the disturbance and the high pressure area to the north generates gale force winds.

Figure 1. Tropical Invest 92L and 0600Z models.

Figure 2. Water vapor imagery depiction of several features affecting 92L.


Tropical Invests 92L and 93L

By: Weather456, 10:52 AM GMT on August 25, 2009

A tropical wave along 64W continues to interact with weakening upper low to produce clusters of deep convection mainly to the east of the wave axis. Convection has become a little more concentrated but remains displaced east and north of any mid-low-level feature due to 30 knots of southwesterly upper winds and thus development should be slow over the next 48 hrs. However, upper winds are expected to become a little more favourable for development over the next 3 days as the upper circulation weakens and is replaced by an upper ridge.

I expect this feature to continue off towards the west-northwest, only slightly feeling the effects of a shortwave trough over the Southeastern United States, which is currently secluding. This should bring the feature close to the Bahamas in about 3 days. Afterwhich, the shortwave becomes amplified by an advancing long-wave trough coming down over the upper mid-west in about 4 days. This should induce a more northwesterly, then northerly component through day 5. Models differ in the timing of these features with the ECMWF and CMC the furthest west affecting the Bahamas and Southeastern United States, while the GFS is the furthest east, well east of the Bahamas and the Eastern United States. Using a blend of the model consensus, water vapour imagery and steering maps, I expect a movement towards the west-northwest to northwest over the next 48 hrs, placing the feature slightly east of the Bahamas. A more northwesterly motion takes over through day 3-5 which may bring the feature close the Outerbanks but remaining offshore. Interests in the Bahamas and the Southeastern United States should continue to monitor the progress of 92L.

Another area of disturbed weather is located in the Southwest Caribbean Sea, also associated with a tropical wave near 83W but there is a low-pressure area attached along the coast of Costa Rico. I expect this feature to move inland over the next 24-48 hrs with little development on the Atlantic side. Regardless, heavy showers will spread across Central America producing up to 5 inches of rain with higher localised amounts. Some of these rains may produce flooding.


Bills becomes extratropical after blowing into the Canadian Maritimes

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

Figure 1. Image overview of Bill's track and the Atlantic Canadian Maritimes. Image credit: Google Earth.

As of 5am EDT, extratropical storm Bill was located near 48.6N-50.2W or 190 miles northeast of Cape Race, Newfoundland, moving off towards the east-northeast at 43 mph. Maximum sustain winds are near 70 mph with a minimum central pressure of 980 mb. Bill has continued to lose tropical characteristics as it enters the extreme North Atlantic, often known as the “hurricane graveyard”. Bill is expected to become a warm seclusion later in its cycle and still poses a threat to the Atlantic Maritimes especially as it nears Europe on Wednesday.

Bill rolled through the Canadian Maritimes Sunday afternoon bringing high wind, heavy rains and dangerous surf. The RCMP had to close off the highway into Peggys Cove due to the danger onlookers were putting themselves in. Three young men were nearly swept away as huge waves lashed the coast for several hours during high tide. Several buoys reported seas in excess of 20ft, with the buoy (44258) just south of Halifax reporting 29 ft seas. Winds along the coast easily reach tropical storm forced but was mainly spared from storm force winds which was located in the front right quadrant which was offshore. Hurricane Bill also dumped heavy rains as its center travelled along the Nova Scotia coast with Yarmouth getting 2.5 inches, while Halifax got 2.17 inches.

By late Sunday Afternoon, 40 000 persons were without electricity but that figure dropped to 270 by Sunday evening, with the remainder being restored by mid-morning today.

Sable Island wasn’t so lucky. Sable Island is located about 180 miles offshore the coast of Nova Scotia and thus received the brunt Bill’s winds and surf. Maximum sustain winds reached 61 mph with gusts up to 77 mph. Buoys nearby Sable Island reported seas of 44 ft and winds gusts of 82 mph. Thankfully, the population of the island is only 5 as of 2008.

After Bill blew through Nova Scotia, it made landfall on Newfoundland’s Burin Peninsula early on Monday but with less steam as it continued to weaken and become extratropical.

Figure 2. Model analysis of Bill between Saturday 12PM and Monday 12am with the brighter colours Beaufort scale 10-12 winds (storm force). Image credit: Magicseaweed.

Table 1. Selected buoy observations along the Canadian Atlantic Maritimes.

Tropical Update

Interests in the Southeast United States and the Bahamas may want to watch a tropical wave currently approaching the Lesser Antilles. All of the global models develops a tropical wave or low-level trough east of the Bahamas and north of Hispaniola later on Wednesday and Thursday and tracks it west-northwest then northwest, before recurving out to sea. The ECMWF has the feature affecting South and North Carolina then moving out to sea. Currently, this feature is interacting with a very broad upper low to produce clusters of moderate to strong convection between 15N-25N just east of the islands. The feature is expected to continue off towards the west-northwest and as the upper low weakens, it will find favourable to marginal conditions near the Bahamas. Regardless of development in the near term, heavy showers will spread across the Leeward Islands later today and continue to move west through Tuesday and Wednesday.

Models are also in very good consensus of another Cape Verde system but there is no organize areas at the moment.

Figure 3. GOES-12 infrared image of the area of disturbed weather being watched and its projected path over the next 3 days.


Bill spares Cape Cod; Heads for Nova Scotia

By: Weather456, 12:20 PM GMT on August 23, 2009

As of 5am EDT, Bill was located near 41.2N-66.5W or 185 miles east of Nantucket, Massachusetts, moving off towards north-northeast near 26 mph. Estimated surface wind are near 85 mph with a minimum central pressure of 961 mb.

Bill is expected to remain on this northeast motion for much of the day as passes along the Canadian Maritimes. By early Monday, Bill is expected to exit Canada into the North Atlantic where it will likely be extratropical already. Some models show Bill becoming a strong warm seclusion that will impact England later on Wednesday.

As category 1 hurricane Bill moved towards the northeast, he remained well to the east of New England, sparing them from the brunt of the tropical storm forced winds. The highest reported winds at Cape Cod were around 26 mph with less than an inch of rain. Bill’s wave however showed little mercy with buoys and coastal stations reporting between 20-30 ft swells, with about 3-5 ft water rises.

Environment Canada is expecting 50 mph winds with seas up to 26 ft. Numerous high wind and rough surf advisories have been posted for the Canadian Atlantic Maritimes with a small craft warning in effect. Rainfall is expected to be between 3-5 inches, similar to Bermuda. This is similar to strong extratropical storms that affect Canada on a yearly basis.

Figure 1. Mounted at the Cable Wharf in Halifax, this camera overlooks the boardwalk at the waterfront. Credit:

What has Bill done so far?

In Bermuda, Bill had very little impact but due to the closure of the causeway (the only access to the airport), flights were cancelled. Some 3,700 households experienced power outages at some point during the storm, and in some instances cable television and internet services were also interrupted, particularly in the central Spanish Point headland. During the daytime on Saturday, public works crews performed cleanup of light debris, mostly discarded garbage unveiled by the storm.

Bill dropped a total of 6 inches of rain on Bermuda, which makes it the 3rd wettest tropical cyclone in Bermuda’s history.

Table 1. Highest recorded rainfall totals in Bermuda since 1939.

Along the United States East Coast, high waves averaging 10ft in height impacted beaches from North Carolina to Maine. In Wrightsville Beach, NC, up to 30 rescues were made due strong rip tides with about two injuries reported. Severe beach erosion and coastal flooding also took place especially on Bald Head Island where 150 ft of beach was washed away, resulting in the loss of the remaining sea turtle nests.

On August 19, Peter Bray, a British rower attempting to break the record for the quickest solo crossing of the Atlantic was forced to abandon his boat and board the RRS James Cook due to being in the path of Hurricane Bill. The image to the right shows Peter Bray rowing out of St. John's Harbour on July 8. He had to abandon his boat this week because of Hurricane Bill. Credit CBC.

Tropical Update

There appears to be three areas to watch over the upcoming week – the Southwest North Atlantic, the Eastern Atlantic and the SW Caribbean Sea, where several models are developing a tropical system in each area. The area in the Eastern Atlantic has plenty of time to watch and develop, but the two areas closer to home will be monitored. The area in the Southwest Caribbean will have to develop quickly due to its proximity to land and that leaves the Southwest Atlantic area with the biggest interest. Models are showing that a low-level trough will develop just east of the Bahamas from either a tropical wave or upper level forcing and drift west to west-northwest in tandem with an upper level trough split. The area then recurves, following a similar path to Bill. There are currently no organized areas of interest out there but the closest candidate is a tropical wave approaching the islands. I will have more on these features over the upcoming week.


Bill Lashes Bermuda; Takes Aim at New England

By: Weather456, 12:29 PM GMT on August 22, 2009

Figure 1. GOES-12 visible image of Hurricane Bill this morning.

As of 8am EDT, Bill was centred near 34.0N-68.4W or about 235 miles west-northwest of Bermuda, moving towards the north near 22 mph. Estimated surface winds are near 105 mph with a minimum central pressure of 960 mb.

Water vapour imagery showed a classic recurvature set-up with Bill moving northerly under the influence of an advancing frontal trough that is currently located along the US East Coast. This should take Bill north-northeast over the next 24-36 hrs with some increase in forward speed. Afterwards, as Bill merges with the entire frontal system during Extratropical transition, amore northeasterly track takes over, in about 48 hrs.

Figure 2. Water vapor imagery showing Bill's location relative to the frontal trough that has been forecast to and will be steering Bill more towards the north and eventually east.


Hurricane Bill delivered tropical storm force winds to the island of Bermuda during the early morning hours of Saturday. The storm also lashed the coast with 20-30 ft waves causing some flooding on the island. Buoy 41048 reported maximum sustain winds of 60 knots with 26 ft peak seas, located just west of Bermuda. The island itself reported peak wind speeds of 46 mph with 60 mph gusts. Rainfall amounts between 20-22 August stands at 0.52 inches, which is not surprising as I said yesterday that Bill is moving pretty fast and thus will not dump a huge amount of rain over the island.

Some roads along Bermuda's northern coast were flooded and traffic was heavy in Hamilton, the capital. The airport, which is accessible only by a low causeway bridge, remains close. All ferry service was also cancelled until Sunday.

East Coast and Canada

Bill is expected to send 20 ft waves from the North Carolina Outerbanks to Nova Scotia later today and Sunday. Numerous high surf warnings have been issued for beaches all along the East Coast and the danger of rip currents is great. The best advice I can give anyone at this time is to stay out of the water. If you are caught in a rip current (as I did, years back), don’t struggle against the current, rather, let it take you until you reach an area where the current has died and then swim back to shore. Much of the buoy reports offshore the Mid-Atlantic States are already reporting around 9-10ft seas and these are expected to increase during the course of the day.

The hurricane is now expected to come close to Cape Cod, Massachusetts, close enough to bring tropical storm force conditions later on Sunday. Waves approaching Cape Cod will be in the range of 20-25 ft with a water rise of 3 ft inland and this could cause some coastal flooding across that area.

Figure 3. Estimated water rise along the coast of New England, if a category 1 hurricane was moving north-northeast near 20 mph at mean tide. The highest water rises occur in Washington and Hancock counties in Maine, similar water rises, maybe even higher is expected to occur along Nova Scotia.

After which, Bill is likely to pass along the coast of Nova Scotia as a category 1 hurricane or a strong Extratropical storm on Monday bringing high wind, surf and rain. More details as Bill moves closer.


Showers and thunderstorms have increase along the ITCZ near 11N, with two concentrated areas near 57W and 35W, likely two tropical waves. The easternmost wave is associated with a 1010 mb low-pressure area that has potential for some slow development over the next day or so. The other wave closer to home will also be watched. Regardless of development, showers and gusty winds will moved through the Southern Antilles over the next 24 hrs.


Bill weakens as it eyes Bermuda

By: Weather456, 10:09 AM GMT on August 21, 2009

Figure 1. Infrared image taken this morning, showing an overview of Bill and the directly and indirectly affected areas.

Hurricane Bill was centred near 26.2N-65.4W or about 425 miles south of Bermuda moving off towards the northwest near 17 mph. Maximum sustain winds are near 120 mph with a minimum central pressure of 951 mb. Due to a slight increase in southerly shear and cooling ocean heat content, Hurricane Bill is looking less organize this morning with the well-define eye feature absent and a ragged western semicircle. Bill however remains a large and powerful major hurricane. I expect Bill to remain above 100 mph over the next day or two as the only inhibiting factor remains falling ocean heat content, which is rather a measure to support major hurricanes not hurricanes themselves.

Bill is currently being steered between a lop-sided ridge at 50W and a weak trough at 75W. I expect Bill to continue off towards the Northwest during today and early Saturday, but begin to curve more towards the north around the ridge by late Saturday; at which point it should be just west of Bermuda. By Sunday, Bill will begin to feel the effects of a strong mid-latitude trough and move more towards the north-northeast then northeast, bringing him more towards the Canadian Maritimes by Monday.

Northern Caribbean and East Coast

Bill is a very large hurricane and thus like Katrina and Ike will displace a great deal of water. Large swells by the hurricane will continue to affect the northern Caribbean from the Leeward Islands to the Bahamas and then spread along the United States East Coast from Central Florida to the Canadian Maritimes from Saturday through Monday. These swells are likely to cause dangerous surf, life threatening rip currents and some coastal flooding. I looked at some of the buoy readings out in the Southwest Atlantic and they range from 9ft just north of Puerto Rico to 23 ft just northeast of the Bahamas.


Bill closest point of approach (CPA) to Bermuda is about 225 miles, while hurricane force winds extend outward 115 miles and tropical storm force winds outward 290 miles. There is no doubt that Bermuda will suffer tropical storm force winds from Bill, preferable in the 50-70 mph range. In addition to high wind, huge waves will lash the island from the south on the order of 22-28 ft. Bermuda is at a lesser risk from storm surge flooding than the Gulf of Mexico because 1) It is an island, and thus the water being pushed by Bill can go around rather than move inland over the Gulf coast because it has nowhere to go, and 2) Bermuda has barrier reefs and high cliffs which should help buffer some of the waves.

However, coastal flooding will still be an issue to deal with. Bill is moving at a very good clip so will not have enough time to dump a huge amount of rainfall over the islamd. The island can expect up to 10 inches of rain from Bill’s outer bands.

The last time a hurricane threatened Bermuda was Hurricane Bertha of last year. The last hurricane to deliver tropical stormed forced winds and/or greater was Hurricane Florence of September 2006. In addition, many remember Hurricane Fabian 2003, a category 4, which passed close to Bermuda.

Nova Scotia and New England

Bill is likely to pass close to New England and Nova Scotia as a category 1 hurricane or an Extratropical storm with hurricane forced winds. Some models show Bill making landfall right along the Canadian Maritimes before heading into the extreme North Atlantic. I will have more details on these areas as Bill gets closer.

Figure 2. Wavewatch 3 significant wave height and swell through 48 hrs showing Bill's large swells will affect basically everyone across the Western Atlantic, with the hardest hit areas being Bermuda, New Engaland and Canada.

Bill’s Size

Bill became one of the largest hurricanes in history when hurricane forced winds extended out to 115 miles. This is only 10 miles shy of Hurricanes Katrina and Ike, whose winds extended out to 125 miles. I’m glad that Bill is in the Southwest Atlantic and not in the Gulf of Mexico or Caribbean Sea.


Models continue to develop an area in the Eastern Atlantic over the next few days and track it west northwest. The only area of interest out there currently is a tropical wave along 28W, which has increase in shower activity. There is abroad area of low pressure associated with this feature so I will be watched over the next day or two.


Bill churns towards the northwest

By: Weather456, 10:03 AM GMT on August 20, 2009

Figure 1. Infrared image taken this morning, showing an overview of Bill and the directly and indirectly affected areas.

At 5am EDT, Hurricane Bill was located near 21.6-60.3W or about 325 miles north-northeast of the Leeward Islands, moving towards the northwest near 18 mph. Estimated surface winds are near 125 mph with a minimum central pressure of 949 mb. Satellite imagery showed Bill cloud tops have warmed somewhat over the past 12 hrs or so but remains an extremely powerful major hurricane. The eye of Bill also remains solid and define and any weakening of large systems, like Bill will be slow to occur. I do not see shear increasing much along the trajectory of Bill but ocean heat content gradually tapers off, indicating Bill will likely remain a hurricane through recurvature.

Bill is now moving towards the northwest based on satellite imagery and this motion is expected to continue over the next 48 hrs. In about 3 days, Bill will begin to feel the weakness by the mid-latitude trough and turn more towards the north-northwest somewhere near 65W, to the west of Bermuda. A northerly component then commences through days 4 and 5 and at which point it may bring the hurricane close to Cape Cod and landfall on the Canadian Maritimes. The closest approach point to Cape Cod will be determined by who meets who first – whether Bill is fast enough to meet the trough or vice versa. My thinking is, they will meet around 65W but the northerly motion of Bill could bring it close the extreme Northeast United States.

Bill is letting his presence be felt in the Islands. Virtual buoy information from Buoyweather.Inc, indicate hazardous marine conditions remain in effect for the Atlantic coasts today with 17 ft seas and 15 mph winds and thus small craft are advised to stay near the coast. Hurricane Bill passed to the southwest of buoy 41044, which is located near 21N-58W. The buoy reported maximum winds of 80 knots, a minimum central pressure of 993 mb and wave heights up to 32 ft.

Similar waves experience in the islands will spread along the Northern Caribbean, US East Coast, but to a higher degree along Bermuda south facing shores and the Northeast United States.

Figure 2. Marine observations from buoy 41044 as Bill passed to its south and west.

Figure 3. Marine forecast for southern Bermuda through the next seven days. Seas peak around 12m (39ft), while gust of tropical storm forced maybe experienced over open waters.

There are no other areas of interest in the Atlantic but some of the models are forecasting the development of another African wave. We’ll see how that goes.

The islands were truly blessed that Bill recurved just in time. Thanks for all the prayers.


Hurricane Bill

By: Weather456, 5:13 PM GMT on August 19, 2009

Figure 1. Visible image this afternoon showing an overview of Bill and the indirectly and directly affected areas.

Over the past 24 hrs, Hurricane Bill put on an impressive round of intensification and has since levelled off as a powerful category 4 hurricane. I can stay here from the Leeward Islands and awe at this giant rather than be terrified by this bad boy. Bill entered a region of marginal ocean heat content and thus would have easily been a category 5 if it was in the Gulf of Mexico or Northwestern Caribbean Sea.

As of 11am EDT, the eye of hurricane Bill was located near 18.7N-56.3W or 610 km east-northeast of the Leeward Islands, moving off towards the west-northwest near 18mph. Maximum sustain winds have reached 135 mph, with a minimum central pressure of 950 mb. Hurricane force winds extend outward up 130 km while tropical storm forced winds extend outward to 280 km, which are well away from the islands. The closest approach point to the islands is 310 km, so some islands may experience gusts of 30-40 mph.

Satellite imagery showed Bill cloud canopy or central dense overcast has warmed some during the morning, thus it is my thinking Bill has peak since ocean heat content will not change much along the trajectory. Bill will however remain a major hurricane for some time to come.

Figure 2. Ocean heat content valid 19 August 2009 with this morning's 11am advisory and projected path.

Bill has finally caught onto the first weakness given its northerly component. It is likely Bill will continue on this course over the next couple of days. Bill is expected to re-curve in advance of a slow moving trough that remains over the Central CONUS and thus will likely thread the line between Bermuda and the United States East Coast through day 5. However, Bill will come very close to the Northeast United States. Bill is expected to transition to a strong Extratropical storm between day 6 and 7 and is expected to affect the Canadian Maritimes.

Bill’s effects will mostly be felt in large swells, large enough to cause beach erosion on the Atlantic facing coasts of the islands. Thankfully, much of the tourist areas and populated beaches remain on the Southwest facing sides of the islands (the Caribbean Sea). Small crafts are advise to stay docked or remain in local waters. Swells of 15-20 ft will then spread towards Bermuda later on Friday and the United States East Coast by weekend.

Figure 3. Wavewatch 3 wave forecasts for 24 and 96 hrs, respectively. 10-15 ft seas will be felt all along the Northern Caribbean, Bermuda and US East Coast


Hurricane Bill: Where is he heading?

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

Hurricane Bill as of 5am was located near 15.5-49.7W moving off towards the west-northwest near 17 mph. Winds have increased to 100 mph with a minimum central pressure of 967 mb. Satellite imagery showed that Bill has probably levelled in intensity for the time being due to an eyewall replacement cycle. After which, the cyclone will probably reach category three status.

Track Forecast

Track has rather become a bit problematic over the last 24 hrs. Currently, steering maps revealed Bill is being steered a deep layer ridge over the subtropical Atlantic. This should result in a west-northwest motion over the next 24-72 hrs. Thereafter, the ridge is expected to split and develop a weakness, which should pull Bill more towards the northwest through 108 hrs. Full re-curvature begins in about 120 hrs as a deeper frontal trough sweeps across the Eastern CONUS.

Now the tricky part is, some models differ on the timing and strength of these features. For the islands, models continue to shift towards the left of the official guidance indicating Bill may not feel the effects of the first weakness and if this continues, Bill could pass close to the islands. Today is probably crucial in determining how close he gets, if he continues west-northwest or finally show signs of moving northwest.

The second trough that is expected curve Bill more north is currently moving over the Central CONUS and with Bill’s forward speed; I’m having a hard time believing it will reach in time to curve Bill either towards Bermuda or east thereof. Bill will likely thread the line between Bermuda and the Eastern CONUS. I’m confident that the trough will be strong enough to allow Bill to miss the East Coast but he may brush close to Cape Cod.

In about 5-7 days, Bill is now expected to heads towards Nova Scotia and it’s a bit uncertain whether Bill will move onshore or pass offshore. Extratropical transitioning of strong tropical cyclones are a threat to the Canadian Maritimes.

Regardless of how close Bill comes to the islands, Bermuda or the East Coast, a swell of 10-15 ft, probably higher will impact the Atlantic facing shores. The islands will probably feel it the worst and coastal beach erosion is possible. In addition, small craft are advise to stay well within local waters as seas could get dangerously rough. Bill is a very large system and like Katrina, Rita, Gustav and Ike, will push a great deal of water.

Yesterday I measured Bill's cloud canaopy in Googlr Earth which was about 480 miles in diameter.

Elsewhere, the remnants of Ana is interacting with mid-upper level cyclonic flow to produce scattered showers and thunderstorms across Hispaniola, the Turks and Caicos and Southern Bahamas. It will be monitored for signs of regeneration as it heads west. Regardless of development, showers will likely spread across Cuba and the remainder of the Bahamas later today and tomorrow.

Another wave is located right along the African coast with excellent mid-level turning and convection within 200 nmi of the axis. Some of the models are indicating that this feature may develop so it will be watched.


Tropical Update

By: Weather456, 10:21 AM GMT on August 17, 2009

Claudette Heads Inland

Tropical Storm Claudette made landfall earlier this morning around 1am EDT on the Florida Panhandle bringing heavy rains and gusty winds, which remained on the eastern side of the system. Radar estimates indicate Claudette may have dumped between 3-8 inches along coastal areas of the Florida Panhandle. Some coastal stations reported winds of 43 knots, which was in line with the official guidance with water level rises of 2 feet above normal. Claudette will continue to draw a surge of moisture as she continues inland and it is possible that an additional 3 -5 inches could fall across the Florida Panhandle and Southern Alabama increasing the risk of flooding.

Ana impacts the Leeward Islands

Ana moved through our local area this morning bring gusty winds and heavy rains. I was rather surprise by the wind gusts, which ventured to tropical storm forced per my personal weather station. About 0.5 to 1 inch of rain fell which probably did help the dry spell but brought one cooler night. Satellite imagery showed Ana continues to fight the long battle with dry air and 20 knots of southerly shear. She will probably continue off towards the west northwest, brining the same conditions to Puerto Rico and the Dominican Republic later today. Land interaction will likely damage Ana severely and whatever is left, enters the Gulf of Mexico in 3-5 days. If a tropical wave or surface trough manages to enter the Gulf, I would certainly not rule another Claudette situation.

Hurricane Bill

Hurricane Bill as of 5am AST is located near 13.8N 44.0W moving off towards the west-northwest near 22mph. Maximum sustain winds have increased to 75 mph with a minimum central pressure of 987 mb. Satellite imagery since the last advisory continues to show a strengthening hurricane and it is likely Bill will reach category 2 status before the day is finished. Bill may reach category 3 status sometime on Tuesday or Wednesday when it reaches 28C waters.

Bill has sped up significantly, as it heads west and somehow may affect its track. Bill is forecast to track west-northwest over the next 1-2 days and then turn more northwest as it nears 50W under deeper layer flow. This is supported by the steering flow and weakness I indicated last night near 50-55W. It is also becoming clear that Bill will not resume a westward track as it heads north of islands as a deep layer trough swings across the Eastern United States through day 5. The threat remains for the Northern Islands and Bermuda if Bill does not strengthen as forecast and heads more west, but the storm will eventually re-curve at some point in its cycle due to the mid-latitude trough to lessen the risk on the United States.


Active Tropics: TD 4; TS Ana; TS Bill

By: Weather456, 12:16 PM GMT on August 16, 2009

Just one week ago, we were tracking what would become 99L. Now we are tracking Tropical Storms Ana and Bill and now Tropical Depression 4, which is, pose to become Claudette later today. I had to open 3 separate internet browser to construct this blog.

Tropical Depression 4

Radar and surface observation clearly indicated a tropical depression had form in the Eastern Gulf of Mexico. Genesis occurred from a tropical wave that interacted with both an upper level system and old frontal system which resulted in a surface trough of low pressure. Convection gradually organize and concentrated over very warmed waters and Tropical Depression 4 was formed.

The tropical depression is located near 27.7N-83.9W as of 8am EDT, moving off towards the north-northwest near 16 mph with a central pressure of 1011 mb.

Radar and satellite imagery revealed a somewhat small but well-define depression producing heavy thunderstorm activity over the center. The system is moving under very light upper winds and very warm sea surface temperatures and it is likely that a tropical storm will form later today, Claudette.

The current motion is north-northwest, and should continue northwestward and reach the coast by later tonight. There have been tropical storm watches and warnings posted for the Florida Panhandle in anticipation of this system. Expect heavy rains, gusty winds and heavy surf within the watch area. Also, do not underestimated TD 4, as things can change quickly. Just ask yourself, how many woke up to a tropical depression.

Tropical Storm Ana

Ana is located near 14.6N-53.8W moving off towards west near 20 mph with maximum sustain winds of 40 mph and a pressure of 1005 mb. Satellite imagery indicates Ana is hanging on for dear life and I doubt it is a tropical storm at the moment. A combinations of southerly shear and dry air is preventing Ana from organizing, rather it remains a very disorganize system. She is still forecast to remain a tropical storm as she reaches our local area later on Monday. Expect squally weather with gusty winds, comparable to tropical waves. Most of the Northern Leeward Islands remain under a tropical watch today.

Beyond the islands, Ana will likely enter the Caribbean and impact the Dominican Republic by Tuesday; in which land interaction will weaken her to tropical depression status.

Tropical Storm Bill

The bigger, better and baddest of the 3 systems, Bill continues to intensify in the Eastern Atlantic. Satellite imagery showed a classic comma band associated with organizing systems. However, cloud tops have warmed over the last few hours. Satellite intensity estimates range from 40 to 50 knots with QuikSCAT revealing 45 knots winds this morning. It is likely that Bill will continue to intensify and become the season’s first hurricane by Monday.

Bill is moving off towards the west near 12 mph. Bill has slowed somewhat and thus will likely reach the weakness in time to pull it north. Nevertheless, how far north? Currently, the official and model guidance are taking the system north of islands but dare I say, this is not over until the fat hurricane sings. More than normal, systems do not end up at their 5-day point. Therefore, it remains unseen whether Bill will affect the islands and United States.

My August forecast called for a 70% chance of 3 named storms, and I guess you know I'm actually smiling, that half way through, the forecast already verified. Well the Atlantic has 2 more named storms to spit out before the month is over.


Double Trouble: Ana forms; TD 3 developing

By: Weather456, 10:39 AM GMT on August 15, 2009

Tropical Storm Ana (left), while Invest 90L (right)

Tropical Storm Ana has formed in the Atlantic, and it is understood that this is rather unexpected since 24 hrs ago it was a remnant low. The first named storm of the season is located near 14.6N 46.8W or 1630 KM east of the Leeward Islands. Estimated surface winds are near 40 mph with a minimum central pressure of 1005 mb. The satellite presentation of this small tropical storm greatly improved during the day on Friday and this was confirmed by a NOAA hurricane hunter plane, which found a well-define circulation and tropical depression winds. This system was re-designated around 12:30am EDT this morning. Currently the system is moving into much warmer waters and shear is 10 knots above the disturbance, unlike what nearly killed it on Thursday. Shear also remains favourable but not ideal and there is the issue of dry air ahead of the disturbance, but some further strengthening remains possible.

The storm is moving to the west but slightly south thereof. The storm will continue west but then turn more west northwest over the upcoming days under the influence of a high-pressure ridge. This system was expected to be a fish storm, now its heading right for the islands and Florida. Tropical Storm Ana should reach the islands in about 2 days then the Greater Antilles by 3 days and the Bahamas by 5 days. According to how close Tropical Storm Ana comes, tropical storm conditions are expected for the Leeward Islands, that is, heavy rains and gusty winds, then will likely spread to Puerto Rico 12 hrs later.

That’s just system number 1. Behind 90L is a more troubling system. Tropical Invest 90L is on the verge of becoming Tropical Depression 3 then Tropical Storm Bill later this weekend. Satellite imagery showed an organizing system with clusters of deep convection wrapping around the center of circulation. Dvorak estimates have climbed to 2.0, which is about 35 mph, which indicate a depression has form or is forming. QuikSCAT also revealed a very define circulation with alteast 30 knot winds. It is likely if this continues, we will have a new depression in the Atlantic today.

Invest 90L is moving west, just as Ana is doing but then will eventually curve more west northwest. In about 72 hrs or 3 days, the models are thinking 90L will be strong enough to feel more of weakness in the ridge and be pull north. The turn northwest is rather sudden on the 06Z runs and that’s why the official track remains south of the global models. This official track brings 90L over Anguilla in approximately 5 days as a hurricane. If 90L continues to track west, the forecast tracks will also shift just like the case with Tropical Storm Ana.

Official Guidance in black

I encourage all in the islands, Bahamas and Florida to monitor the progress of both Ana and 90L. Review your hurricane plan today and get your needed supplies. Those in the islands know it only takes a tropical wave to cause major flooding problems. In addition, listen to what your local mets are saying because it likely watches may go up today or on Sunday.


Tropical Invest 90L organizing

By: Weather456, 10:03 AM GMT on August 14, 2009

A tropical wave along 75W south of 25N is interacting with a very broad upper low over the Western Caribbean to produce scattered showers and thunderstorms across the Southwest North Atlantic. This moisture is currently spreading across Hispaniola parts if Cuba, and the Bahaman Islands. Most models show this tropical moisture will head west into the Yucatan, Western Cuba, Florida and the Southeastern United States later over the weekend. Development does not seem likely now but will continue to be monitored.

What was Tropical Depression 2 has been downgraded to a remnant low due unfavourable upper winds and dry air. It is likely Ex-TD 2 will continue west within a shallow steering flow and may re-strengthen into a tropical depression if it is able to meet favourable conditions. There have been some increase in shower actvity along this feature so I will continue to monitor this system as it has potential to develop quickly near 50W. It should be just northeast the islands in 3 days.

Tropical Invest 90L is estimated be located just south of the Cape Verde Islands, maybe west of there as it continues off towards west. Invest 90L continues to become better organize with increase in shower activity and a reduction in the size of its circulation. Much of the heaviest convection remains on the eastern edge of the circulation but with isolated bands elsewhere, similar to 90L in August 2007 which became Hurricane Dean. Shear remains 5-10 knots with a stationed upper anticyclone above; and sea surface temperatures of 28-29C. I expect the disturbance to continue organize later today and could become a depression anytime this weekend.

Most of the models agree on an intensifying tropical cyclone, probably becoming a hurricane next week. The 00Z NOGAPS though, opens the feature but still has it near the islands. Most models have the feature moving off towards the west through 3-5 days, then turning west-northwest then northwest in 5-7 days. This motion brings it near the islands as a tropical cyclone by Wednesday/Thursday next week. Only the ECMWF has it missing the islands and that is because of its slower evolution and feeling more of the weakness in the subtropical ridge. Both the GFDL and HWRF, hurricane models, bring 90L to major hurricane as it nears the Leeward Islands. Overall model consensus has shifted a bit north, that is if 90L does not continue west.

Those in the Northeast Caribbean should continue to monitor the progress of 90L. It is likely we will be dealing with this for some time to come. In addition, regardless 90L affects the Caribbean or United States, still be prepared. Don’t wait for an event like 90L to start preparing. Here’s a hurricane checklist.


TD 2 weakens; 90L is trouble

By: Weather456, 9:58 AM GMT on August 13, 2009

Tropical Depression 2 was located near 14.0N 36.9N, moving off towards the west near 12 mph. Estimated surface winds are near 30 knots with a minimum central pressure of 1007 mb. Anyone with two eyes can see this depression has weakened considerably over the past 24 hrs. Shortwave infrared imagery showed the expose low-level circulation with little associated convection. This system has been undergoing 15-20 knots of easterly shear and guess where it is originating. The easterly shear that is affecting TD 2 is coming from the upper anticyclone over 90L. Interesting stuff. Tropical Depression 2 may eventually escape the clutches of 90L over the next 48 hrs and still has a chance to make it to tropical storm strength.

The weakening of TD 2 has not surprisingly led to a more southerly track. If you remember from my update yesterday and Tuesday, I pointed out the difference between the shallow and deep layer flows. This system will still feel the weakness and pull north but may still entirely miss it. I think the Northern Leeward Islands should monitor the progress of TD 2 based on the trend; as if we don’t have enough on our minds already.

Tropical Invest 90L

Tropical Invest 90L is born. Satellite imagery analysis along with QuikSCAT revealed a well-define but somewhat large mid-low level circulation near 11N-21W moving slowly off towards the west. Showers and thunderstorms have slowly been increasing around the system but has a skewed look due to a vigorous anticyclone located above. The disturbance is moving over 28C waters with SAL non-existent and with the upper anticyclone; conditions appear perfect for cyclogenesis over the next 24-48 hrs. The models continue to develop this system rapidly has it heads west over the next 4 days. While the models agree on intensity, they differ greatly in timing and track. The GFS/CMC/ECMWF/UKMET and GFDL all have a slower guidance, indicating the system will make it to the Antilles in 1 week. While the NOGAPS quickly pull the system north under a faster guidance. The ECMWF has also been trending north of the islands. The forecast steering flow shows a ridge north of 90L for at least the next 5 days, so a westward movement is expected. Beyond 5 days, the system may turn a bit to the north, but it will be too late as the system is already located at 50W. I will continue to monitor the progress of 90L but I employ folks in the islands to be vigilant in times like these. Do not panic, but stay on top of updates. The Weather Channel will be broadcasting the tropics most of the time today.

Impact of the United States is also a possibility but alot of IFs this point in time.

I did not plan a Hurricane Charley anniversary blog but on this day, 5 years ago, Charley roared ashore South Florida causing unimaginable devastation. I tracked Charley from start to end, and still has the largest forecast error to date with that quick turn. If you have any stories or comments about your experience with Charley, I invite you to post them.


Tropical Depression near TS strength; Trouble A'brewing

By: Weather456, 10:31 AM GMT on August 12, 2009

As of 5am this morning Tropical Depression 2 was located near 14.6N 32.4W moving off towards the west at 12 mph. Estimated surface winds are near 35 mph with a minim central pressure of 1006 mb. Satellite imagery revealed the center is just slightly on the edge of the heaviest convection, but the overall structure of the depression remains well organize. Satellite intensity estimates from ADT, AMSU, and SATCON range from 45 to 50 knots, indicating the satellite presentation of the system would probably support a tropical storm. In addition, QuikSCAT pass this morning revealed 35-knot rain contaminated wind barbs in the front right quadrant.

Conditions appear ripe for continued organization and strengthening but the long-term intensity of the system remains uncertain as some models show the feature encountering a bit of easterly shear as it nears 60W in 5 days. However, the majority of the models show only slight weakening as a result but enough to keep the feature a tropical storm. The future track of the system mainly depends on how strong it gets. The shallow steering flow has less weakness at 40/50W than the deeper layer flow. Therefore, a weaker system is likely to continue on a more southerly track, while a deeper system will likely shift a bit north. I will continue to go with the official and model guidance but will not rule out the Northern Leeward Islands yet.

Trouble is brewing off the coast of Africa, in association with a very large area of disturbed weather. I was surprise that the National Hurricane Center and the Weather Channel both caught onto this feature, but I guess it is hard to ignore the computer models. There is a broad area of low pressure located along 18W or just along the coast of West Africa that has potential to develop over the upcoming week. A very large and potent circulation was evident on satellite imagery emerging off the coast. With the exception of the NOGAPS, all of the global models and GFDL develop this wave and none is less vigorous than the next. The ECMWF/GFS/CMC all have a hurricane impacting the Lesser Antilles late next week. This is one to really watch.

Elsewhere, a tropical wave continues to move along 50W south of 18N. Limited shower activity remains associated with the wave as heads west towards the Lesser Antilles. This feature will be watches as some models have it entering the Gulf of Mexico in 4-5 days. Regardless of development, isolated showers are likely to continue to spread across the islands later today and tomorrow.


Tropical Depression 2 arrives; TD 3 soon to follow

By: Weather456, 10:48 AM GMT on August 11, 2009

More than 2 months has pass since we had our last depression and certainly one of the longest gaps within a hurricane season since 2004, not Alex, but between Nicole and Otto. Satellite presentations greatly improved overnight with Dvorak readings reaching 2.0, 35 mph and 1006 mb. In addition to satellite imagery, QuikSCAT revealed a well define low-level circulation last evening. It is without a doubt that a depression has form. I expect this system to continue to gradually strengthen under favourable conditions and likely become “the long awaited Ana”, as it continues towards the west.

My current thinking on track remains unchanged from yesterday. Much of the global guidance continues to take this system west-northwest, then bit west over the next 72 hrs (3 days) and this is also in agreement with the latest steering flow. The NHC center stated in the forecast discussion that a weakness in the subtropical ridge could induce a west-northwest motion in 3-5 days. If for some reason this system continues to more west than normal, it could eventually affect the Northern Leeward islands but current official forecast takes it north thereof.

There are a few other areas of interest out there, the first being a tropical wave entering the Eastern Caribbean. This tropical wave brought heavy squalls as it cross the Southern Antilles yesterday and is now continuing west. I do not expect much from this area over the next 24 hrs.

The second area of interest is another wave nearing 50W south of 17N. The wave is displaying very well define mid-low level cyclonic turning along the axis near 13N. Showers remain somewhat limited but with 5-10 knot vertical shear and 28C waters, the system has some potential to organize over the next day or two.

The third area of interest is a wave over West Africa that most global models continue to develop and intensify to atleast a strong tropical storm later this week. The GFS is the most aggressive, bombing out the feature to a major hurricane as it nears the Caribbean next week. While we cannot guarantee these kind of scenarios so far out, the success of model support with 90L, TD 1, 98L and TD 2; could mean a new depression will likely form in the Atlantic later this week or next week.


Tropical Invest 99L; Felicia Weakens; Record Flooding

By: Weather456, 10:31 AM GMT on August 10, 2009

Tropical Invest 99L

As of 0900 UTC, Tropical Invest 99L is estimated to be located near 15N/24.5W moving off towards the west-northwest near 10 knots. Winds are estimated to be near 25 knots with a minimum central pressure of 1008 mb. The center of the system is currently moving over the southern Cape Verde Islands.

This morning satellite and QuikSCAT imageries continue to show a well-define mid-low level circulation associated with the disturbance but with much of the convection remaining in the southern semicircle of the system. The system continues to slowly organize, at best, since it has not change much since Sunday. Environmental conditions remain conducive for organization and development of this system but it could enter some cooler waters near 26C as it nears 30-35W.

Much of the global guidance continues to take this system west-northwest, then bit west over the next 72 hrs (3 days) and this is also in agreement with the latest steering flow. The uncertainty arises in 120 hrs or 5 days when the system reaches the mid-Atlantic. Some models show a more pronounce weakness in the ridge than others resulting in a gradual turn out to sea (GFS), but others show no such weakness and take the system more westward over the Northern Lesser Antilles (CMC). The weakness is effectively being cause by a mud-upper ridge but I do not think it will be as pronounce as the GFS. However, I still cannot put much faith in the CMC southerly track based on 99L current motion. My judgement in these cases mostly depends on the vapour flow of the atmosphere using water vapour and TPW loops that shows a west-northwest, then gradual westward movement over the next 5 days. However, this motion, though far north, still places the storm near the Northern Leeward Islands. It will mostly depend on the timing and strength of the weakness so I will continue to monitor the situation.

Figure 1. Regional global model guidance for 99L as of 0600 UTC 10 August 2009.

Felicia ripped to threads

Felicia is now a ghost of her former self after encountering strong upper winds, which ripped the thunderstorms clear off the low-level circulation. However, Felicia still has enough thunderstorms with it to produce heavy rains (up to 2 inches) once it reaches the islands over the next day and flash flooding remains a possibility. Felicia has also built up a large swell, which has already reached some of the islands. The last report was that some beaches have been close in anticipation of the tropical cyclone’s effects.

Figure 2. 6-hr forecasted precipitation ending 2PM 11 August, local time. Credit: National Weather Service, Hawaii.

Typhoon Morakot

Typhoon Morakot which is now weakening over Southeastern China has left a trail of destruction and devastation in its wake mainly across Taiwan. The typhoon struck Taiwan late on Friday and has since then dropped over 100 inches of rain over the past three days causing one of the worst flooding the island has experience in 50 years. Morakot is blamed for injuring 15 across Taiwan, with at least six other people either dead or missing. The Philippines also continues to clean up after outer rain bands from Morakot were blamed for causing numerous floods and landslides, killing 10 and injuring at least 18 others.

Morakot will likely continue to weaken today but will also continue to dump heavy rains across China. Some places could expect up to an additional 4 inches of rain, which will likely increase the chances of more flooding.

Figure 3. Three-day 24 hr rainfall totals from August 8-10 local time, which is August 7-9, Atlantic time. Credit: Taiwan Weather Central

Rainfall Records

Wei Liao Mountain recorded a total of 114 inches of rainfall over the course of this event. This makes Typhoon Morakot the wettest tropical cyclone in Taiwan’s history surpassing Typhoon Herb in 1996. Morakot also has the record for the tropical cyclone with highest 24 hr and 48 hr rainfall accumulation. This is the highest rainfall total I observed in my short life and it probably broke the 48 hr record held by Réunion Island.

Figure 4. The top 22 highest reported rainfall across Taiwan during the past 72 hrs from August 8-10, local time or August 7-9, Atlantic time. Some of these rainfall amount exceeded 2m or 2000 mm. Credit: Taiwan Weather Central

Flooding caused a hotel in the south of Taiwan to collapse, after rising water is thought to have caused the foundations of the building to become unstable.


Eastern Atlantic wave; Felicia to bring heavy rains

By: Weather456, 10:51 AM GMT on August 09, 2009

A broad area of low pressure in associated with a tropical wave is now approaching 20W and while the latest satellite imagery showed a reduction in convective coverage, the area continues to possess a well-define mid-low level circulation. This morning QuikSCAT pass also revealed a closed elongated center of circulation which in agreement with the latest visible imagery. The overall structure of this wave surpasses many we had during the 2009 Hurricane Season.

The disturbance is estimated to be located near 13.5N, which is a west north-west movement since it emerged over Africa. An upper anticyclone* has developed over the system (which is a first for 2009), and it is moving over 27-28C waters. It is likely this feature may continue to organize in the season’s second depression.

All of the model guidance develops this feature; the last time a saw so much model guidance for an African wave was either Josephine or Ike of 2008. Most of the models take the system west to west northwest along the southern periphery of the Bermuda High. However, the GFS quickly takes this feature out sea and that is because the GFS is seeing a more pronounce weakness in the subtropical ridge due to a split in the TUTT. I would go with the model consensus. We should not worry so much about track, as the nearest land areas (other than the Cape Verdes Islands) is 7 days away. However, I employ persons in the islands to just check up on this feature and monitor its progress.

There is another wave over the continent that the models have already begun to develop, that is the CMC and GFS. This effectively doubles the chances a Cape Verde system affecting someone out west. This seems like the beginnings of the upswing in the Cape Verde Hurricane Season I predicted earlier.

The last area of interest is the wave approaching the islands. It should bring some showers to the islands later today and Monday but maybe be involved in some tropical activity in the Western Caribbean, Gulf or near the Bahamas later this week or next week.

A flood and tropical storm watch has been issued for the Hawaiian Islands in anticipation of Felicia. It is unlikely she will be a hurricane by the time she arrives Monday night, so we can rule out any wind action. However, rain will still be a major problem. Sometimes these weaker systems cause more damage than hurricanes since they start to “rain out themselves” resulting in torrential rainfall.

I will continue to monitor all these features and have an update on Monday.

*An upper anticyclone aids in the upper level outflow of a system and can also buffer it from strong wind shear. It is one of the features that I look for when determining the degree of development of a system.

I posted 4 new pics to the right if you would like to view and rate them.


Here We Go Again

By: Weather456, 10:56 AM GMT on August 08, 2009

Showers and thunderstorms have increased in association with a surface trough 600 miles east of Barbados. Much of this shower activity remains somewhat disorganize and associated with the ITCZ but to a lesser extent than a few days ago. In addition, satellite imagery and 850 mb vorticity maps also showed an improvement in the low level struture of the trough. However, upper winds are only marginal for development, but could improve over the next few days as the feature reaches the islands by Monday/Tuesday. Regardless of development, scattered to isolated showers will spread across the islands starting as early as Sunday.

The other feature of interest is an emerging tropical wave located along 13W. Satellite imagery and surface observations revealed well define mid-low level turning evident along the wave axis. Environmental conditions are much more favourable than past waves, as SAL remains well to the north of the disturbance and shear is about 5-10 knots with an upper anticyclone in the eastern MDR. Most of the global models, with the exception of the ECMWF, try to develop this area. The ECMWF has been doing pretty well this season, so I would like to see this model come onboard in regards to development. In addition, I’m not entirely sold on development until the wave fully emerges and persists for atleast a day or two.

I will continue to monitor these two features and have an update on Sunday.


A Google Earth Tour: The Caribbean

By: Weather456, 9:35 AM GMT on August 07, 2009

The tropics remain relatively quiet with nothing expected through the weekend. Hurricane Felicia continues to churn in the Eastern Pacific but remains days away from the Hawaiian Islands. The central Atlantic surface trough/wave should reach the islands by Monday and will be discussed more in detailed in my next blog.

Google Earth is a virtual globe, map and geographic information program that have gained popularity since it was discovered in October 2005. Today, I am going to take a tour of the Caribbean using images rendered in Google Earth.

The Bahamas

We begin in the Bahamas, which is a group of atolls and cays in the Southwest North Atlantic that developed due to the exposure of coral reefs from declining sea levels. Over thousands of years, ocean currents transport sediment, which were deposited along the exposed coral reefs, which built up to form islands, atolls and cays. The spectacular image below revealed the tops of the expansive coral reefs to be the Bahamas we know today. The largest island slightly left of center is called Andros Island with Nassau just to the northeast. The Florida Keys, Caymans, Anguilla and Barbados are among similar islands.

Image 1. An aerial view of the Northwesern Bahamian Islands.


Haiti has one of the worst hurricane histories in the Caribbean with over 4000 deaths recorded in the last 2 decades with most notable storms being Hurricane Gordon 1994, Hurricane Jeanne 2004 and Hurricane Hanna 2008. The number one cause of these deaths is not necessarily the wind and storm surge, but the torrential rains. Most of Haiti’s hill slopes have been the subject of deforestation since the arrival of the Europeans, who used the trees as timber to build some of the first settlements of the New World. Centuries later, Haiti hill slopes have become barren and with lack of root support, landslides are easily caused when excessive rains falls.

Image 2. Haiti's hillslopes viewing north from the capital of Port-au-Prince. Notice the vegetation-barren hillsides.


This island is located just to the southeast of Saint Kitts and Nevis and possesses one of the most active volcanoes in the Caribbean, the Soufriere Hills volcano. A series of devastating eruptions between 1997 and 1995 buried the island's capital, Plymouth, in more than 12 metres (39 ft) of mud, destroyed its airport and docking facilities, and rendered the southern half of the island uninhabitable. The image below illustrates the aftermath of the eruptions, with the easily identifiable brown areas, being mud, ash and pyroclastic flows.

Image 3. A view of the island of Montserrat after the 1995 and 1997 eruptions which covered two thirds of the island in ash, mud and pyroclastic flows.


Aruba is an island in the Southern Caribbean just offshore of the northern coast of South America and is part of the “ABC” islands, the other two being Bonaire and Curacao. Aruba‘s climate is very dry due to a number of factors. First, Aruba constantly lies within the northeast trades, north of the equatorial convergence zone and cloud maxima. Second, these trades are stronger than normal; especially when the Colombian Low is enhanced, thus contributing to upwelling of waters offshore the South American coast and contributing to further stability. The third reason is the continental dry air that is sometimes advected off the mainland and over the islands. The fourth and last reason is the geography of the islands, which eliminates the possibility of relief rainfall as in mountainous areas.

Image 4. From this image you notice the lack of luscious biomass instead you notice sparsely distributed shrubs and other plants that thrive in dry weather.

I hoped you enjoyed this short tour of the Caribbean using the technologies of Google Earth. If you do not yet own Google Earth, you can download it here to see these and other wonders of the world. If nothing significantly changes in the tropics this weekend, my next blog will be Monday or Tuesday.


Normal Season Still Expected; Hurricane Felicia

By: Weather456, 10:31 AM GMT on August 05, 2009

The broad area of disturbed weather located to the Southwest of the Cape Verde Islands has significantly diminished in shower activity over the past 24 hrs. Satellite imagery revealed some cyclonic turning still evident along the feature but its chances of becoming a tropical depression remains low as it tracks west. It will be monitored for any changes. Some models continue to forecast some development with this feature and another wave over Africa.

Hurricane Felicia

I don’t normally mention Pacific storms unless they pose some threat to land and Hurricane Felicia could. The latest advisory placed her as an intensifying 90-knot hurricane and there is room for further intensification. The latest GFDL model run and the NHC projected path place Felicia just to the east of the Big Island of Hawaii but it is unlikely that she will be a hurricane at that time due to sub-26C waters. It is likely she will cross the Hawaiian Islands as a weak tropical storm or depression by early next week. When you have a system like Felicia and previously Lana come near to Hawaiian waters, that is good indication of an El Nino. The last time this occurred was in 2006 and 2004.

Hurricane Felicia (Right)

Mid-Seasonal Forecasts

I was a bit surprise at the numbers issued by Gray and TSR yesterday and I am eagerly awaiting the National Oceanic and Atmospheric Administration (NOAA) numbers, which is the one I prefer out of all seasonal forecasts. I was surprised that after a quiet June and July that only 1 storm was subtracted from Gray forecast. Ironically, they previously called for 11 named storms, which is the long-term average but dropped one storm on 4 August, which is the June/July average. Tropical Storm Risk Inc. (TSR) on the other hand raised their numbers to 13 named storms due to warmer sea surface temperatures (SSTs) than previously thought. This seems like a milder version of 2004. On 4 August 2004, TSR issued their mid-season prediction stating, “This season has more to offer with a 150% chance of a US landfalling hurricane”, while all others lowered their numbers and landfall probabilities. They predicted 14 named storms, with the season actually giving 15. They also did well in 2007 and 2008.

With the development of El Nino, it is likely that this season will not venture much into October and November, so the thought of 10-13 named storms between August 15 and September 30 is not rather quiet at all. When you have a clustering of storms like that, it is likely the steering flow will change for 1 of them, so this season might seem like a dud now, but look out when the next MJO arrives.


Tropical Update

By: Weather456, 10:19 AM GMT on August 04, 2009

Before I discuss the main feature of the day, a surface trough of low pressure is located just north of Hispaniola does not necessarily have to the potential to develop into a tropical system but has the potential to bring increase moisture to the Bahamas and Florida later his week as it interacts with a secluding upper low. I will continue to monitor this feature.

A broad area of low pressure located near 32-33W continues to produce significant thunderstorm activity in and around the vicinity of the ITCZ. Satellite presentations of the system greatly improved over the past 24 hrs with broad mid-low level turning evident along the trough axis. There has been evidence that a bit of easterly shear maybe affecting the system since the low-level reflection appears east of the heaviest thunderstorm activity, but otherwise, presents itself as one of the more organize disturbances of 2009.

Currently, some of the model guidance like the 00Z CMC, UKMET and GFS have initialised this area as a broad area of low pressure and is hinting development. However, they appear well off, from where the actual trough is. That is where the ECMWF comes in, which initialises this feature at 32W as of 00Z 4 August (or 8PM last night). Based on the present motion and the forecasted mid-low level steering flow, a west to west-northwest motion is expected over the next 3 days. Afterwhich, the feature could turn a little more towards the northwest and should near the Islands by Monday. Models continue to differ on the strength of the system as it tracks west, with some have it as an open trough while others have a tropical system.

The only environmental variable that this feature will have to contend with in the near term is dry air. If it can manage to build a moisture shield, then it stands a chance. Vertical shear is expected back off towards the west while SSTs become progressively warmer. However, we still have the issue of the ITCZ, so keeping in mind, there is 30-40% chance of some slow development over the next couple of days.

There is another feature over West Africa that appears to be associated with another strong tropical wave. It will be monitored as it emerges.

The recent activity in the Eastern Pacific can be teleconnected here in the Atlantic Basin later this week and for much of August as the MJO continues to pulse towards the Western Atlantic. The long-range GFS continues to show multiple Cape Verde systems active at the same time indicating an increasing environment for cyclogenesis is coming.


Tropical Update

By: Weather456, 12:08 PM GMT on August 03, 2009

Happy Monday to all,

I continue to monitor a broad area of low pressure located just south of the Cape Verde Islands that has the potential to develop into some later this week. Satellite imagery revealed the feature is most likely a tropical wave with a classic inverted V pattern in the cloud clusters. It also showed the dry airmass north of the system continues to suppress convection and keeping the wave confined to the ITCZ. Despite this, most of the reliable global models are hinting that this area, along with the help of another area of low pressure along the coast, may develop into a tropical depression and track west. Most models agree on timing, over the next 24-36 hrs, but disagree on the strength and track.

Basically, the feature has yet to show any significant signs of development and thus will remain relatively weak. The system is also embedded within the ITCZ and along with the shallow to mid-level flow, favours a westward movement. This should effectively keep the feature south of most of dry air and with wind shear remaining favourable from now through Saturday, has the potential for some slow development. However, there is currently a low chance since models have not agreed on the strength of this disturbed area, likely due to the uncertainty of African Dust.

I will continue to monitor the feature as it track west. If it does not develop, it should reach the islands by Saturday as a tropical wave.


August Outlook

By: Weather456, 10:10 AM GMT on August 02, 2009

I will not comment much on the eastern Atlantic development since much remains unchanged over the past 24 hrs. Some of the models (GFS, ECMWF) continue to hint development of a vigorous mid-level feature over Africa that will emerge today, and while I do think some slow development is possible, it’s still a “wait and see” situation, especially since the models have been back and forth on this.

July Summary

Activity during July 2009 was near or slightly below both the long-term and 1995-2008 average. Normally, there is an average of one tropical cyclone per year during the month but there were no storms recorded during this year, which makes it one of the latest starting seasons and the first time since 2004 when June and July went without a named storm.

Unlike June, vertical shear did not take precedence over all other factors, as it was not as high as in June. Large amounts of African dust and higher pressures were the main contributors to a more stable tropical Atlantic and Caribbean. The only factor that stood mainly favourable was the continued rising of sea surface temperatures and ocean heat content which at one point, rivalled 2005. My July forecast called for a 50-60% chance of atleast 1 named storm, mainly in the latter half, which did not verified as we ended up with only three invests. The likely cause of this forecast error was the amount of dust forecasted. Despite calling for more dust than June, I also indicated that it would be below normal. That did not occur and many well-developed waves weakened due to dry air.

Extratropical Invest 94L

This featured developed from a non-tropical low that meandered across the Central Subtropical Atlantic though July 2-5. This disturbance was under very high vertical wind shear during most of its life but was able to get deep convection over its center of circulation early on July 4. Shortly after the low level center began to track south and the convection continued towards the northeast, which highly decoupled the whole system. The system passed south of the Azores between July 6 and July 7 and never caused any significant damages.

Tropical Invest 97L

I myself do not know how we ended up from 94L to 97L, but the first invest to develop in the deep tropics originated from an impressive tropical wave, which emerged on July 14. The system was designated an invest while to the southwest of the Azores on July 16. Over the next few days, the system remained weak and convection-deprived due large amounts of surrounding dry air and was deactivated on 18 July. On 19 July, as the feature approached the Windward Islands, it suddenly began to become better organize and was reactivated. However, the system never acquired a closed circulation and eventually entered a high shear environment the next day. The system remained disorganize as it passed the Windwards and head into the Eastern Caribbean. The system was deactivated for a second time after passing Puerto Rico and Hispaniola. Though the system was never named, it brought gusty winds and heavy rains to the Southern Antilles, Puerto Rico, Dominican Republic and Haiti. Rainfall amounts exceeded 5 inches in some spots.

Non-Tropical Invest 98L

Non-tropical Invest 98L was a short-lived invest which developed offshore the US East Coast on 23 July. The system originated from a non-tropical low which was aided by vigorous tropical moisture which streamed north with the help of 97L. The system moved up the US East Coast over the next day or two at which time it impacted the northeast United States with tropical storm-like conditions i.e. strong winds, heavy surf and rainfall. Radar signatures resembled a transitioning tropical cyclone.

Figure 1. Tropical Activity for the Atlantic basin during July 2009.

August Outlook

August is fairly more active than June and July, in fact, climatology states that activity ramps up during the first two weeks of August. An average of 2-3 tropical storms develops annually in August with four named storms forming by August 30. Most of the variables such as wind shear and sea surface temperatures are expected to be much more favourable this month but given that the MJO is expected to remain in a suppressive state until atleast 10 August, there is a 70% chance of atleast 3 named storms with an 80% chance of one of those becoming a hurricane.

Figure 2. Track of all tropical cyclones occurring in August between 1851 and 2006 showing a significant increase in storm numbers and distribution.

Sea Surface Temperatures

A negative North Atlantic Oscillation (NAO) was observed for the entire month of July, which acted in favour of warming sea surface temperatures (SSTs). During a negative phase, the subtropical ridge becomes weaker than normal which reduces the speed of the trades and results in less evaporational cooling. There is one particularly area of the Atlantic which did not escape the effects of tradewind cooling and that was the Southern Caribbean Sea just offshore the South American coast where easterlies were enhanced by the Colombia low, rather than suppressed. It is likely that sea surface temperatures and ocean heat content will continue to rise due seasonality and that NAO is expected to enter neutral-positive.

Figure 3. Operational SST Anomaly Charts (C) for July 30 2009 from NOAA/NESDIS. Most of the Atlantic remains near normal or above normal especially off the coast of Africa.

Vertical Shear

The presence of El Nino was felt across the Gulf of Mexico and Caribbean Sea as shear was above normal for the most parts during July. This strong shear prevented any sustainable convection from developing such as with 97L (above). Surprisingly shear remained near to below average for the tropical Atlantic during this same period. The latest GFS model run through 17 August 2009 showed a much more favourable upper pattern in the Gulf of Mexico and tropical Atlantic but remaining a problem in the Caribbean for the next two weeks due to the tropical upper tropospheric trough (TUTT). It is likely that promising tropical waves moving off the coast of Africa will find a favourable upper pattern to develop and track west if they remain north of the Caribbean area. As August progresses, this pattern changes and the entire basin becomes conducive for TC genesis, which is typical as we approach the peak of the season.

Figure 4. GFS wind shear forecast through August 14 2009.

The Madden Julian Oscillation (MJO) and Saharan Dust

Early last week, I posted a blog entry on the low global tropical cyclone activity recorded in July, mostly in regards to the MJO. I outlined that the downward state of the MJO has been suppressing tropical convection across the tropical Atlantic and Africa, which is likely contributing to a more stable atmosphere. In addition, the suppression of tropical rainfall over Africa is causing an increase in African dust and subsidence is increasing the high pressure, which is driving the dust west.

Just as the MJO has been suppressing tropical activity over the tropical Atlantic for the past month, it can easily enhance tropical cyclone activity. The GFS is showing a suppressive MJO through August 16, which is unlikely since both the EWP and CFS models show neutral to upward pulses of the MJO around the 10th. This is also in agreement with the “probability tropical cyclogenesis” which increases dramatically through August. The latter model did very well in June and July as it predicted little activity. Signs of the MJO presence have been observed along Central America and Mexico. This upward motion of the MJO also coincides with the climatological decline of African dust, which peaks in July.

Steering Flow

The pattern observed for much of July favoured the recurvature of any tropical system that might have threaten the United States East Coast with persistent low-pressure troughing over the Eastern United States (figure 5). The GFS 500 mb forecast through 18 August and the CFS monthly averaged through 29 September shows a persistent trough-like pattern remaining in place over the Eastern United States. This pattern is rather contradictory to the observed North Atlantic Oscillation pattern, which idealistically should show a weaker than normal Icelandic Low. The synoptic pattern also seems to be in favour of the Gulf Coast with persistent high pressure remaining in place across Southern Plains. This should effectively keep storms south thereof but does increase the risk for the Caribbean, particularly, Central America. Despite this ideal set-up, one should not let their guard down; should the pattern break for a week could mean the difference between a quiet season and a not so quiet season.

Figure 5. July 500 mb observed anomalous heights showing lower than normal heights across the Eastern United States and a higher than normal heights across the subtropical Atlantic. This is a conceptual model of a positive NAO and yet the NAO observed for July was negative. This seems to indicate some differences in what is actually occurring and what atmospheric modelling is showing. Image credit: Bureau of Meteorology, Australia.

Figure 6. Climate Forecast System (CFS) 500 mb monthly average through 29 September 2009 with the orange dashed line depicting the semi-permanent East Coast trough and the red arrows showing the resultant storm tracks. Image Credit: WxCaster


I would say that this August will be near the long-term average which dictates about 2-3 storms will form this month. The reason why I cannot say a less than normal August will occur is because the tropical atmosphere has been showing signs of changes since the last week of July. There is a 70% chance of atleast 3 named storms forming this month and it is likely that one of those storms will be a hurricane. However, it is likely this hurricane season will not have more than 10 named storms due its slow progression, as we should have had about our second named storm by this point in time. Activity during a particular season is not correlated to landfall so everyone should still be prepared.

Happy Emancipation (celebrated the first Monday in August) to all the Caribbean folkes out there.


First day of August

By: Weather456, 10:18 AM GMT on August 01, 2009

Currently the entire tropical Atlantic is quiet, but I doubt it will stay that way for long as now the global models have latched onto a very well structured wave over Africa. A tropical wave is estimated to be located near 9W moving off towards the west near 10-15 knots. Satellite imagery showed a well structured wave with mid-low level cyclonic turning evident along the axis and is likely this feature has a mid-level circulation. However, little or no significant convection accompanies this wave. Most of the models agree that the wave will emerge over the next 24-48 hrs, with the GFS, CMC and UKMET calling for a tropical depression to form. I don’t really see any inhibiting factor that might deter the wave except for the larger scale effects of the MJO. The Saharan Air Layer has disperse for the most parts and the forecast calls for low levels over the next 3-4 days; sea surface temperatures where the wave is expected to emerge is about 27-29C and wind shear is running 5-10 knots across the Eastern Atlantic. As with all strong tropical waves over Africa, this one is very vulnerable when it comes to the oceanic environment of the Eastern Atlantic and thus development is uncertain until it emerges. In addition, I would like to see if other models come onboard or if those three models back off development. Despite this, conditions appear conducive for something to develop.

I do encourage tropic-lovers to be patient with this hurricane season since it’s not that uncommon to have such slow progression. It’s just that many are accustomed to past active seasons, especially since the blogs started. My August outlook is schedule for tomorrow. In the meantime, if you have any questions about the season, leave it here and I will get back to you through Wunder email.


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.