Weather456's Tropical Weather Blog

Tropics Quiet; Tropical Invest 90L Revisted

By: Weather456, 10:38 AM GMT on June 30, 2009

The tropics remain quiet and the models are not showing anything for atleast the next week. There are a few interesting tropical features in the Atlantic this morning. First, water vapour imagery showed a vigorous upper trough/low spinning over the Caribbean helping to generate some scattered showers and multilayer cloudiness across the Eastern Caribbean. Second, is a tropical wave near 30W south of 15N is moving off towards the west near 10-15 knots. This wave remains void of any deep convection but has excellent cyclonic curvature in the low-mid level cloud field of the Saharan Air Layer. I will continue to monitor the wave as it spins west. It should near the islands by weekend.

Tropical Invest 90L revisted

Probably one of the most disputed invests in a long time. Tropical Invest 90L was a disturbance than formed south of Cuba and drifted north over the Bahamas where it was absorbed by a frontal trough over the Florida Peninsula. During genesis of the new system, the pressure gradient between it and high pressure to the north produce high winds and rough surf. The system also dumped heavy rains across the Bahamas, Florida and the Southeastern United States. As the storm neared landfall it possessed a few characteristics that would have classified it as a named storm.

You can download the full report of Invest 90L in either Word 2007 format or PDF format.

Word 2007

PDF Format

Let me know what you think.

Weather456

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Tropics Quiet; July Outlook

By: Weather456, 10:40 AM GMT on June 29, 2009

Tropical Update

Tropical Invest 93L is gone, and it really took the other 50 and not develop. Satellite imagery show a few low level moisture in the vincity of ex-93L and even though some scattered showers maybe enhanced along this feature over the next day, development is not expected as it moves off towards the west-northwest.

The African wave the models were forecasting develop has not been entirely dropped but instead of closed low, they are now showing a strong tropical wave moving west. While it is unlikely the wave will develop in the Eastern and Central tropical Atlantic, I'm still going to monitor this one as it enters the Western tropical Atlantic and Caribbean this weekend as it now enters the July climo of the Eastern Caribbean.

There are no other areas of interest and models are not showing anything for the balance of the month.

June Summary

Well, we are now at the end of June and activity for the month was near the long-term average, which sees one named storm every other year. Even the mighty year, 2005, saw only two tropical storms during the month. However, this is the first time since 2004 when we did not had tropical storm activity for June if we include Arthur, which formed May 31 2008; indicating even though activity was near the long-term average, it was relatively quiet compared to recent years.

Vertical wind shear took precedence over all other factors during the month, due to southern extent of the subtropical jet. Sea surface temperatures were above normal, and even above 2005 levels in the Eastern Gulf and around the Bahamas. African dust saw only 2-3 outbreaks for the month, which is typically a peak period for dust. We should have had least one tropical storm based on the conditions, but wind shear blew strong and fierce and in such way, it hindered convection along tropical waves approaching the islands. June ended up with only two tropical invests.

Tropical Invest 92L formed near the Azores on June 02 and meandered slowly NNE producing gale force winds. In my tropical update on June 04, I hinted that this invest gained subtropical characteristics and was likely a subtropical storm, but SSTs below the disturbance was below the criteria for subtropical cyclones, probably the reason it was not classified. I still hold to this day, it was a subtropical storm.

Tropical Invest 93L developed from mid-level energy that moved north into the Caribbean on June 25 and interacted with a passing tropical wave. The area moved towards the northwest and across the Yucatan, emerging over the Gulf of Mexico on June 29, where it later weakened due to an upper low in the vicinity.


Figure 1: Tropical/Subtropical Activity for June 2009.

July Outlook

I am expecting a near normal July, which suggest about more than half the hurricane seasons see their first named storm by July 11. Due to a downward pulse in the MJO and marginal wind shear, offset by above normal SSTs and continuation of below normal dust events, there is a 50-60% chance that a tropical storm could be named this July, with its best likelihood of occurrence after July 16.


Figure 2: Track of all tropical cyclones occuring in July between 1851 and 2006 showing the majority of storms were clustered and tracked in the Western Caribbean and Gulf of Mexico but points of origin stretched further east than June.

Sea Surface Temperatures

Sea surface temperatures did remarkable warming during the months of May and June and were above the long-term average for most parts but not as warm as previous years in the Main Development Region (MDR). With the lack of convective and dust activity and a negative North Atlantic Oscillation (lighter trades) continuing into July, I expect a continuation of warming in the Atlantic with SSTs remaining above the climatological mean but below previous years in the MDR. One of the most noticeable warming occurred in the Eastern Gulf of Mexico and around the Bahamas, where SSTs were above the levels of 2005!


Figure 3: Operational SST Anomaly Charts (C) for June 25 2009 from NOAA/NESDIS. Notice the Main Development Region (MDR) remains cooler than normal but SSTs in the Western and far Eastern Atlantic remain warmer than normal.

Vertical Wind Shear

Vertical wind shear was mainly controlled by a ridge-trough-ridge pattern, with upper ridging over the Eastern CONUS/Mexico/Western Atlantic and the Eastern Atlantic, while troughing dominated within across the Caribbean and Tropical Atlantic. This created a band of heavy wind shear (the subtropical jet stream), which persisted across those regions for much of the month. During the month of July, the Tropical Upper Troposphere Trough (TUTT) is expected to be near its climatological mean, which is a bit more favourable than June was.



Figure 4: GFS 200 mb analysis (top) and forecasted wind shear (bottom) illustrating several features that controlled wind shear across the basin for June and will control it for July.

The Madden-Julian Oscillation and Enhanced Rainfall

The Madden-Julian Oscillation (MJO) is expected to enter its downward phase during the first 2 weeks of July after spending almost 3 weeks enhancing rainfall across the Western Atlantic. This is the main reason why I’m not expecting much during this period. It is not to say that tropical development cannot occur but the potential decreases in the downward phase of the MJO. Enhanced rainfall is expected to return to the Western Hemisphere during the latter part of July into early August and thus coupled with other environmental conditions, the chances greatly increases during this period.

Saharan Air Layer and African Rainfall

This remained below normal for June with about 2-3 dust outbreaks recorded during the month. A weaker African Easterly Jet (AEJ) over Africa contributed to weaker tropical waves, and as we saw in my May 31 blog entry, tropical waves are responsible for helping the dust propagate from West Africa into the Tropical Atlantic. Above average rainfall over Sahel also contributed to lower dust levels, which defied my seasonal forecast. The same pattern is expected to continue into July but with waves becoming more frequent and stronger, I expect a little more dust this month than June, remaining below normal however.


Figure 5: Seasonal rainfall anomaly for Sahel showing wetter than normal precipitation for both Western Sahel and Sub-Sharan Africa. The former is where much of the dust forms and exits while the latter is where much of the waves form.


Figure 6: MODIS TERRA image taken on June 24 2009 at 1810 UTC showing a conceptual model of the Saharan Air Layer (SAL) across the Atlantic with the ITCZ and tropical waves on its southern periphery. The dust stretched from Africa to the Lesser Antilles in one continuous band.

Steering Flow and the North Atlantic Oscillation

The North Atlantic Oscillation entered a negative phase during the month of June and is expected to continue to do so, contributing to lighter trades and less evaporational cooling of the Atlantic sea surface. This also implies a more centralised, weaker tropical ridge and a pattern similar to 2008. A weaker high also implies less northward stress on the ITCZ which is now along 8-10N. Troughs will not be as prevalent along the US East Coast during the first two weeks. If we do get a storm forming in the Atlantic, a westward track would be ideal based on these parameters.


Figure 7: Forecast of the location where the 500 mb pressure surface will be at a height of 582 decameters (5280 meters) above sea level based on the GFS and the position of the subtropical ridge for the month of July based on the CFS.

Summary

Climatology says that more than half of hurricane seasons see their first named storm by July, with a smaller percentage by August (1992, 2004, et al). I am expecting a near normal July due to marginal vertical shear and a flip-flop MJO offset by above normal sea surface temperatures and below normal dust. There is a 50-60% chance that a named storm will form this month, the chances probably higher during the latter half of July.


Weather456


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Tropical Invest 93L over the Yucatan

By: Weather456, 12:27 PM GMT on June 28, 2009

Based on multiplatform satellite winds and surface observations, Tropical Invest 93L is located over the Northern Yucatan Peninsula near 21N-87W moving off towards the NNW. Satellite imagery this morning showed a very disorganize system, likely due to land interaction and a wedged breathing room in the upper layers caused by two upper level circulations on both sides of the tropical invest.

Due these factors, not much development is expected today until the system moves over the Southern Gulf of Mexico in the next 36 hrs. During this time, both upper level features are expected to move away and allow an upper ridge to build more over the tropical invest causing a more favourable upper environment. This all depends on how long the system remains over the Yucatan and how quickly the upper level circulations exit the region. The latest water vapour imagery showed 93L would not survive if it moves in sync with the upper low.

The westward movement associated with 93L moving over the Yucatan has now caused implications in track. Previously, the models agreed that the system would move north into the South-eastern Gulf and quickly recurve into Eastern Florida, and even the NHC guidance agreed. Now, the guidance has shift west for several reasons, including the current position and the fact that it might not get picked up by the first frontal trough, but a second one. This would cause it to move further west than previously thought and recurve further north. This is not expected to be a fast moving system, spending 5 days to reach the coast. Conditions are forecast to become somehwat favourable for development over the Gulf for the next 48-72 hrs, so it still stands a chance before vertical shear increases in about 72-96 hrs. For now, the most we can do is monitor the situation, and it can reach anywhere from Mexico to the Florida Panhandle, which includes Texas and Louisiana.

Regardless of development, the disturbance will continue to produce a few scattered showers over the Yucatan and Western Cuba later today.



East Atlantic

Most of the global models continue to forecast the development of a tropical wave over the Eastern Atlantic by Monday. Currently there are no organized wave systems in the vicinity but a couple of wave axes evident. Any feature forming out here would move due west under persistent deep layer flow south of the ridge. The models quickly develop the wave but weaken it in the Central Atlantic due to cooler waters. Most models decrease shear enough to allow development but I don’t know how a wave would survive a climatologically unfavourable area. I will continue to monitor this area.

Weather456



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Tropical Invest 93L Dumps Heavy Rains

By: Weather456, 11:33 AM GMT on June 27, 2009

Alot has change since I posted my blog about 24 hrs ago as the area of disturbed weather in the Northwest Caribbean is now Tropical Invest 93L and intensity and track which was previously uncertain is now becoming more evident.

Tropical Invest 93L was located near 20.0N-83.4W with winds of 25 knots and a pressure of 1009 millibars. I choose the centre that was closest to the lowest reported pressure in the area. Satellite imagery indicated motion is NNW around 8-10 mph. The imagery also revealed the heaviest convection remains east of the suspected centre due to some southwesterly shear from an upper low over the Bay of Campeche. This should slow development and organization of the system today until it enters the Gulf of Mexico where the upper environment is expected to be more favourable for development as the upper low exits the region.



What has 93L done so far?

Since the best track data started around 1200 UTC 25 June 2009, the disturbance has dropped copious amount of rain across the Western Caribbean, particularly Nicaragua, Honduras and the Caymans. Satellite and model estimates indicated 100-150 mm (3-5 inches) of rain fell across the area with isolated amounts up 200 mm or 7 inches! I scanned some of the personal and official weather stations but few reflected this rainfall amount and I have not seen any reports of flooding yet. Since the convection of 93L was for the most parts concentrated, Jamaica and other surrounding areas did receive much rainfall.



Where will 93L go and what will it do?

Tropical Invest 93L is expected to continue off towards the north-northwest over the next 24 hrs, which should bring it near the Yucatan channel by tonight or early on Sunday. The heaviest rains may still be east of the centre over Western Cuba but by then the upper low maybe too far west to influence the system. I do not expect much of the system during this time, except for heavy showers and gusty winds for Cuba and the Yucatan. These areas could expect up to 2-4 inches over the next 24-48 hrs.

As the storm enters the Gulf later tonight, the trouble begins. The upper low has cleared the area allowing for a more favourable environment, and coupled with scorching SSTs, development of the system is likely and it could become a depression or tropical storm. I am giving this a 50% chance of doing so by Monday, the highest I gave for any system outside 90L and TD 1. I do not see anything that would hinder the storm except some shear that will accompanied a frontal trough in 96 hrs. It should be noted that not much of the reliable computer models initializes or develops this area and that is likely due to the lack of definite low-pressure circulation.

The storm will be begin to feel the effects of an advancing frontal trough and veer towards the east by Tuesday and head towards the west coast of Florida mid-next week. I cannot pin point an exact location but folks along the Gulf coast should monitor the system. I will have another update shortly when visible images become available.



East Atlantic

I will be monitoring the East Atlantic also over the next couple of days as now the four reliable global models UKMET, ECMWF, GFS and NOGAPS develop a tropical wave by 1 July. The models have been reasonable with this, in that, they keep the system near 10N; near the warmest SSTs and decrease a large area of shear. I gave this a 25% chance of occurring for now mainly due to climatology.



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Western Caribbean Disturbance

By: Weather456, 10:53 AM GMT on June 26, 2009

The Atlantic remains quiet this morning with just one area of interest to speak of. Deep convection continues to increase across the Western Caribbean in association with a mid-level disturbance, which is beginning to interact with a westward moving tropical wave near 82W. The latest satellite images revealed mid level turning on the western edge of a line of deep convection over Nicaragua/Honduras, extending offshore. Surface observations did not show much in terms of wind shifts but a western Caribbean buoy near the disturbance showed a sharp drop in pressure, over the past six hrs.

Current analysis indicates that the disturbance lies below favourable anticyclonic flow with vertical shear near 5-15 knots and above SSTs near 29C and thus will be monitored over the next couple of days. The system appears to be drifting northward but a northwest to west-northwest motion is expected under the influence of deep layer ridging over the Atlantic. This should take the system over the Yucatan by Sunday and emerge over the Gulf of Mexico by Monday. Most of the global models agree on this near term solution so slow development, if any, will occur due land interaction. Beyond 4 days, they are in less of an agreement on where the system will go, with the NOGAPS & GFS taking it into the Western Gulf, while the CMC takes it towards the west coast of Florida as deeper system. Since development is uncertain at this point, I will have to go with the GFS and NOGAPS solutions, which takes the system across the Central Gulf in a NNW motion over the next 4-7 days. It should be noted that anything organize entering the southern Gulf of Mexico in 4 days will encounter favourable conditions, as an upper low currently over the Yucatan shifts west and weakens, allowing upper ridging to take over. Currently, the NHC gives the system a less than 30% chance of development and I agree since we have no surface low yet and only two of the reliable models develop this system; two things I would like to see.

Regardless of development, heavy showers will continue across the Western Caribbean today, including the Caymans, Cuba, and possibly Jamaica today, and spread west across central America and the Yucatan Peninsula on Saturday and Sunday. Locally heavy rains of 2-4 inches are expected.

A tropical wave is near 21W south of 15N moving west near 15 knots based on TPW loops and a partial QuikSCAT. The GFS has been forecasting development of this area for several days now. I’ll continue to track this wave as it moves off towards the west for signs of it taking off.

Weather456





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Strongest Wave of the Season but little expected

By: Weather456, 10:53 AM GMT on June 25, 2009

There a couple areas to discuss this morning but nothing of imminent threat. Firstly, the broad area of low pressure I’ve been looking at in association with the surface trough draped across the Southwest Atlantic continues to linger for the most part. A surface low is expected to develop along this feature within the next day and move quickly off towards the northeast as a non-tropical gale between a trough over the Eastern United States and a ridge over the Central Atlantic. It is becoming more unlikely that anything subtropical will become of this area but it did bring a good amount rain to the Bahamas and Southern Florida. Unless any significant changes occur, this is the last time I will discuss this area.

A tropical wave is currently located in the Central Caribbean just south of Hispaniola moving off towards the west near 14 knots. This wave has increase in some forward speed and is expected to move into the Central Caribbean by weekend. Currently, the wave is producing low-level shallow moisture but limited deep convection. Some of the models are indicating that this wave may seek to increase some low level vorticity as it nears the Yucatan Peninsula and take a weak low level disturbance northwestward across the area. Anything forming will not move too much northward as a potent high pressure ridge builds westward over the Gulf of Mexico. I will continue to monitor this feature but regardless of development, some low level moisture may spread across Jamaica and the Caymans later today or Friday and then showers across Mexico, Cuba and Belize through the weekend.

Probably the best looking and most define tropical wave of the season is along the coast of Africa. This wave was previously analysed near the prime meridian about 24 hrs ago but recent low-level winds revealed the wave maybe located further west than previously indicated near 7-8W. This feature is expected to emerge over the Eastern Atlantic over the next 12 hours, about the same period as the 06Z GFS, which quickly develops a tropical wave by this time Friday. I’m still not inclined to believe this solution yet since none of the other models agree with the GFS and it’s not a climatologically favoured area. Environmental conditions remain marginally favourable at best over the Eastern-Central Atlantic and these waves tend to fall apart after they emerge over cooler waters. Conditions are expected to become increasingly favourable near 50W, with low vertical shear due to the seclusion of the TUTT and above average SSTs but that remains mid-next week. My best judgement on the available data can be summarize as saying that a strong tropical wave will emerge over the Eastern tropical Atlantic over next day or two and while, little development is expected this feature will be monitored.

A second African wave is expected to emerge over the Atlantic next week and the model also develops that feature.

Weather456



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Hurricane Andres Left At Least One Dead; Early Start to Cape Verde Season?

By: Weather456, 10:49 AM GMT on June 24, 2009


Tropical Storm Andres briefly became a hurricane yesterday afternoon as the hurricane hunters found supporting winds and pressure, including a Dropsonde that revealed 66 knots (76 mph) surface winds. During this time, a weak eye-like feature appeared at the centre of an anaemic looking tropical cyclone, likely due to dry air entrained from the Mexican Mainland. Its closest approach to the Mexican coast was 65 miles at 5 pm EDT yesterday with sustain winds of 75 mph.

Andres dumped up to 8 inches of rain along Mexico’s southwest coast and brought rough surf to many coastal resorts from Manzanillo to Puerto Vallarta, which toppled trees and left at least 1 dead.

Currently, the tropical cyclone is located near 19.5N/106.7W, moving off towards the northwest near 9 mph with winds of 60 mph and minimum central pressure of 996 mb. Some forward increase in speed is expected and gradual weakening as the storm enters the more stable environment of the Eastern Subtropical Pacific Ocean.



Atlantic

There remains only one interest area in the Atlantic basin this morning. The tropical wave nearing the islands has lost much of its shower activity and was not expected to develop, however, radar imagery showed the wave still producing scattered showers across the area. This wave will be watch as it enters the Western Caribbean over the next couple of days.

The broad area of low pressure in the Bay of Campeche also lost much of its shower activity but while moving inland and was able to drop a few showers according to surface reports.

The last area continues to be a broad surface trough of low pressure draped across the Southwest North Atlantic to the Southern Florida Peninsula and the Eastern Gulf of Mexico. Some models and the TPC guidance continue to show the development of a low pressure along this surface trough over the next day or two. The area is expected to move off towards the northeast by day 3-4 under the influence of deep layer steering between a trough over the Eastern USA and a ridge over the Central Atlantic. This is the only area of much interest right now and still depends on how much time it has to become something significant.

An early start to the Cape Verde Season?

Probably not. The GFS has been indicating that several strong tropical waves will emerge over the Atlantic over the next week. The latest African Easterly Wave Analysis revealed several tropical waves over the African continent and to the untrained eye; it may appeared to be otherwise. However, the feature responsible for generating the tropical waves, the African Easterly Jet; is currently in a relative strong phase right now. There is a wave near 0E and another near 20E. The GFS is indicating the former will emerge over the Atlantic on Friday and develop into a close cyclone by Sunday. While wind shear and SSTs near the disturbance is expected to be favourable, there is one major probably; the model initializes and develop the low at 5N which is too far south for cyclogenesis. By Monday, the cyclone is near 10N in the Central Atlantic, which is a little more reasonable but SSTs there are on the borderline to support tropical development. The GFS continues to gradually strengthen the system as it nears the islands by July 1. I will have to continue to monitor this odd situation but none of the models has really agreed with the GFS’ solution or time frame.

In my opninion, I'm highly skeptical at this point in time about the GFS solution especially after the runs it made this month. At this point I'm looking for model consensus and signs of a strengthening tropical wave. Otherwise, this remains a strong tropical wave.

The other wave near 20E is strong and is forecast to reach the coast on Monday as one, if not, the strongest wave of 2009. The GFS also develops this feature but not as strong.

Weather456





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Tropical Update

By: Weather456, 11:04 AM GMT on June 23, 2009

Three areas I’m looking at this morning in the Atlantic:

First, a tropical wave is tilted from 62W to 59W, south of 20N moving west near 10-15 knots. Satellite imagery show much of the heaviest convection remains displaced east of the wave axis due to strong westerly upper winds. None of the models develops this feature, as wind shear remains unfavourable for atleast the next 3 days. Thereafter, this feature is expected to enter the Western Caribbean where shear may let up enough for this feature to be monitored closely. Regardless of development, moderate to heavy showers and possible thunderstorms will spread across Barbados, Northeastern South America, Trinidad and the Southern Windwards later today and on Wednesday.

The second area of interest is prefrontal trough of low pressure, which is generating clusters of heavy convection over the Bahamas and southwest North Atlantic. Most of the models agree that a surface low will develop along the decaying frontal boundary over the next 24 hrs and move off towards the northeast under the influence of Central Atlantic High Pressure over the next 3-4 days. This area is rather interesting as it appears to be genesis along a dying frontal boundary. According to how quickly it develops and moves off towards the northeast, it stands a chance of becoming an area of interest, as environmental conditions will allow it.

The third area of interest is a surface trough of low pressure situated in the Bay of Campeche. Last night QUIKSCAT pass revealed sharp low level turning along the trough but with the absent of deep convection at that time, only light winds were found. This morning’s satellite imagery showed cluster of showers along this feature and though the surface reflection remains evident, these showers remains somewhat disorganize. Wind shear is a low 5-10 knots over the area and thus some development is possible as the area moves into Veracruz over the next 24-36 hrs, bringing with it, scattered showers.

Some of the models are hinting that the tropical wave over the Eastern Caribbean may help to energize the genesis of a surface feature in the Western Caribbean over the next 3-5 days and moves north into the Gulf of Mexico. Currently not impossible but translate to more rain until we get a surface low down there.



Tropical Storm Andres

This morning’s satellite images of Andres continue to show he is strengthening with winds now up to 70 mph and a central pressure of 990 mb. At 5AM he was located near 17.4N 103.4W moving off towards the northwest at 8 mph.

On this present motion, Andres should pass very close the Mexican coast throughout the day, bringing with it hurricane conditions, that is, high wind, high waves and heavy rains which could cause coastal & localised inland flooding.

Andres is expected to begin to turn away from the coast early on Wednesday and enter the more stable environment of the Subtropical East Atlantic, gradually weakening within each period, 3-5 days from now.

I’ll have some more updates on Andres and his effects at noon.

Weather456



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Tropical Storm Andres & The Atlantic

By: Weather456, 10:36 AM GMT on June 22, 2009

The first named storm of the Eastern Pacific season formed late last night and is now located near 15.0N/102.1 west or about 190 miles south of ZIHUATANEJO., Mexico. Tropical Storm Andres is moving slowly off towards the west northwest with sustain winds near 50 mph and a central pressure of 997 millibars.

This morning satellite imagery showed continued improvement in the storm’s structure with a central dense overcast embedded with ¾ banding features. The storm is has two excellent outflow channels both poleward and zonal, with the latter being enhanced by an upper trough over the Caribbean. The storm is moving over waters near 30C and under modest vertical shear. Thus, further strengthening of Andres is expected and he could become a hurricane later on Tuesday, maybe even sooner at the current rate of intensification.

During this time, Andres is expected to move off towards the northwest-west northwest, remaining offshore but close enough to bring tropical storm conditions (winds in excess of 40 mph, heavy rain and rough surf) to the Mexican coast resulting in tropical storm advisories listed along the coast.

By Wednesday, the storm begins to track more westward away from the coast, weakening with each period as it enters the stable environment of the Eastern Subtropical Pacific with drier air and cooler sea surface temperatures.

I will post another update around 7 this evening and you can check back throughout the day as I post updates within the comment sections of my blog.



Atlantic

Currently, a cold front is draped across the Western Atlantic from Georgia to an extratropical low in the extreme Northwest Atlantic. I’ll be watching the tail end of this frontal boundary over the course of the week as some models are hinting that a low-pressure area may develop near the Bahamas later on Wednesday. None of models takes this system to a non-frontal warm-core system and it is expected to quickly move over waters less that 26C as it races northeast, so chances of it becoming something subtropical or tropical is slim at the moment.

Another area of interest is an area of convection that surge northward from the eastern Pacific over the Tehuantepec Peninsula and the Bay of Campeche, associated with some of the energy from the precursor of Andres. If this area continues to pull north, it would meet somewhat favourable conditions in the Bay of Campeche. Some of the models deepen a low-pressure area over the area and move it into Mexico “Bret 2005 style.” Regardless of development, heavy rains are expected over Oaxaca, Tabasco and Veracruz. I’ll continue to monitor this area.

A tropical wave is currently near 54W south of 15N, moving towards the west near 10-14 knots. Current satellite images show clusters of deep convection along and to the east of the wave axis. Upper winds are too unfavorable to allow development of this feature over the next day as it tracks west. The wave will however bring showers to the Southern Windwards and Trinidad later on Tuesday.

Weather456



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Summer Is Here!; Tropical Update; Other Stuff

By: Weather456, 12:21 PM GMT on June 21, 2009

Tropical Update

The Atlantic remains quiet with one area being watch in the Eastern Pacific. Firstly, an upper level high pressure (Continental Heat Ridge) is situated over the Eastern Plains. Dry air is being funnelled around the south and western flank of this feature helping to bring dry and fair weather to the Gulf of Mexico, and south-central/eastern United States. Mid-upper level moisture is being advected from a stationary frontal boundary further north around the eastern flank of the ridge over Florida and Southwest North Atlantic. This ridge has been responsible for bring seasonally warm temperatures to the Southeast United States over the past week with departures from average reaching 8F.

Fast upper winds and relatively dry air stretch across the Caribbean and into the Tropical Atlantic not just due to an upper trough north of our area but because of the outflow jet emanating from 93E in the Eastern Pacific. The only areas of showers across the region appear in isolated lingering moisture and convection over Central America associated with 93E.

Satellite imagery showed two tropical waves in the tropical Atlantic this morning. The first one is along 45W south of 15N moving west near 10-15 knots. This wave is accompanied by an excellent inverted-V pattern within clusters of convection on both sides of the axis. This tropical wave is probably along the ITCZ, which had finally made a leap north to 10N! This tropical wave will probably reach the southern islands by Wednesday/Thursday bringing a small/modest increase in moisture to Northeast South America, Trinidad and the southern Windwards. The probability of rainfall exceeding 1 inch this week over these areas remains 45-50%.

The second tropical wave is along 20W south of 10N, with little associated convection.

None of the reliable models seem to forecast anything for the last week of June. They were hinting development along the tail end of a frontal boundary but the area seemed to become absorbed too quickly to allow any significant development. The western Caribean will probably be watch during the last days of June into July.



Eastern Pacific

Tropical Depression 01E came ashore early Saturday as a poorly disorganized system but brought heavy rains to parts of Mexico. On June 19, 2.44 in (62 mm) of rain fell in Mazatlán, near where the remnants of the depression moved ashore. High winds in Mazatlán knocked down several trees, cutting power to numerous residents. Heavy rains also triggered street flooding throughout the city. Landslides along major roadways caused several accidents, one involving a bus that was damaged by rocks.

Another area of disturbed weather is located about 155 miles south of San Marcos, Mexico. This morning’s satellite imagery showed a well defined low pressure system with clusters of deep convection in and around the centre. However, the system remains broad and large and will take some time to coalesce and thus gradual development is expected over the next 3 days. It is likely that this system will become the season’s second depression but aside from the development, heavy rains will continue for Southern Mexico and parts of Central America with some areas under moderate to severe flood potential. I will continue to watch 93E as it moves off towards the west northwest.

Summer is here!

Summer began around 05:45 UTC/01:45 EDT today June 21 2009 and runs until September 22. Summer is the best season of the year, in my opinion, because it is probably the time when persons become more active outdoors in either gardening/yard work, beach, picnic, barbeques, pool parties and sports. Today is the longest day in the year and the shortest night. Astronomically speaking, the ecliptic (apparent track of the sun across the sky) is 23.5 degrees higher in the sky than the celestial equator. It also marks 24 hrs of daylight for areas north of 66.5N including parts of Alaska, Canada, Greenland and Russia. Meteorologically speaking, it is the warmest season of them all; when air mass thunderstorms are more prevalent; and probably most known for an increase tropical cyclone formation in the tropics.

Hope you enjoy this summer!


Other Stuffs


I will be issuing my July outlook next Sunday, June 28 2009 and preliminary estimates indicate that we may see little activity by 15 July as the subtropical jet continues to linger along 20N, during the first week of July but I will have see how the second week goes on the Sunday model runs.

Vertical shear for June was extremely above average for areas south of 20N due to the position of the subtropical jet, which continued to branch anonymously south for June. Areas north of 20N experience near average to below average shear (where the jet had split) and that is where Tropical Invest 92E formed at the beginning of the month. This pattern is similar to May 2009. Contrastingly, sea surface temperatures and Saharan Dust was near/above average and below average, respectively.

I had a tropical cyclone report prepared for Tropical Invest 90L, but my home PC crashed and I lost the file. However, I had some back up data and I will try to work on it this week. Included in the report is the synoptic history, meteorological data, damages/causalities and graphics. It should be noted in the report; the best track data listed 90L as 35 knots peaked winds at landfall around 1200 UTC May 23 2009 near the Alabama/Mississippi Border. It also include a list of buoy data over the span of the invest’s life, with several buoys reporting 30-35 knots winds as 90L neared the coast. Tropical Invest 90L was not only windy but also wet with 12+ inches reported in some locals.

Reports in both 91L/01L and 92L will be issued later with 92L probably the most interesting report. I included a summary map below of all the tropical activity for the year. These maps are based on best track Invest files from the NOAA FTP servers and are used in the tropical cyclone reports.

If anyone was wondering how the tropical cyclone reports will look, here is a download link to Severe Tropical Cyclone Hamish from earlier this year.

Weather456



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TD 01E Heads for Mexico; Atlantic Remains Quiet

By: Weather456, 10:52 AM GMT on June 19, 2009

Tropical Depression 01E continues to head quickly for the West Coast of Mexico with winds near 35 mph. The latest advisory has it near 19.7N 107.1W or about 245 miles south of Mazatlan, Mexico, moving towards the north-northeast near 12 mph.

The latest satellite images showed the tropical depression is feeling the effects of southerly shear east of an upper trough extending from the Wes Coast of the United States, with the heaviest convection remaining well north of the centre, almost along the coast. Heavy rains are likely affecting Islas Marias, a group of islands offshore the Mexican coast.

There is still a good possibility that the depression is upgraded to a tropical storm prior to landfall, as shear remains marginally favourable and sea surface temperatures in excess of 28C. Regardless of tropical storm classification, the depression will spread heavy rains across parts of the Nayarit and Sinaloa states. A band of additional moisture may spread further north across the Northern States of Chihuahua and maybe the south-central United States. Generally, 1-3 inches can be expected with localised amounts of 4-5 inches.





Atlantic Basin

The Atlantic basin remains and none the models are showing tropical cyclogenesis over the weekend, however, models are hinting an increase of low-level vorticity along a frontal boundary draped across the Southwest North Atlantic over the upcoming days so I will monitor that area. Now let’s see what’s going on:

A broad upper ridge extends from Mexico into the South-Central United States and across the Southeast United States while a broad upper trough extends from the Southwest Caribbean to the western tip of Cuba. Dry confluent flow is being funnelled in between the two features across the Western Gulf of Mexico with more moisture available within a diffluent zone across Cuba, the Bahamas, Florida and Southwest United States.

Meanwhile, the subtropical jet is digging deep into the tropics and is helping to generate a band of showers along the length of Central America as it rounds the base of an upper trough across the Caribbean. This position is unusually south for the jet in late June. The jet then exits the region west of 70W, where weak diffluence aloft is generating mid-upper cloudiness and isolated showers over the Eastern Caribbean.

Over the next day, the heaviest rainfall will be found along Central America and Northern South America due to the combine effects of the ITCZ, daytime heating and upper diffluence. Additional rains may be found over Cuba and Hispaniola due to daytime heating and upper diffluence. Smaller amounts due to isolated low-level moisture will be found elsewhere.

Weather456



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First Eastern Pacific Storm to Affect Mexico

By: Weather456, 10:42 PM GMT on June 18, 2009

The first tropical depression, and likely the first tropical storm of the Eastern Pacific Hurricane Basin is heading towards the West Coast of Mexico. This afternoon’s public advisory had the storm located near 16.3N and 108.2W or about 360 miles south-southwest of Mazatlan Mexico. The depression is moving off towards the north near 7 mph with tropical storm watches posted along the coast.

Visible imagery throughout the day showed the storm had encountered some northwesterly shear but has regained much organization as it moves under an upper anticyclone. The depression is also moving over sea surface temperatures in excess of 28C and I expect it to strengthen into a tropical storm over the next 12-24 hrs.

Forecasted motion should be about north-northeast between a deep layer trough extending from the Western Coast of the USA and a deep layer ridge over Central America. This should bring it along the coast in about 48 hrs or Saturday, local time. Expect gale force winds with gust of tropical storm force and heavy rains (up to 3 -5 inches per 6 hrs) mainly in the front right quadrant of the storm. Some flooding is possible.

I will have an update Friday morning on this system and the remainder of the Atlantic. My next blog was supposed to be Sunday but we have a system that is expected to affect our friends over in Mexico. I will post a Spanish version also.

Weather456

Current and past track, tropical storm watches and wind profile for Tropical Depression 01E



GFDL Forecast Model through 48 hrs



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Tropical Update

By: Weather456, 10:47 AM GMT on June 17, 2009

Broad upper ridging continues to support upper divergence along a broad area of low pressure that comprises a surface trough near 91W and a tropical along 88W which is leading to a broad area of disorganize showers over the Yucatan and surrounding areas over the Northwest Caribbean and Eastern Bay of Campeche. This area of low pressure is expected to drift slowly west into the Bay of Campeche over the next day or two bringing additional rains to the Gulf Coast of Mexico. During this time, conditions are expected to be somewhat favorable to allow development, so the system will be monitored.



An area of low pressure has enveloped along a frontal boundary offshore the eastern United States. This may or may not be the area of low pressure the models are forecasting but another gale force low is expected to develop along the same frontal boundary later on Friday. While it is uncertain whether these features will become something subtropical in nature, seas of 5-7 ft will impact the Eastern United States, especially North Carolina. Some models have the area of low pressure lingering along the coast but generally moves it towards northeast over the weekend.



These 2 areas will be monitored for significant changes, otherwise, My next blog will be Sunday which is the official start of Summer. It is also the time frame in which the GFS is showing the development of a strong tropical wave in the Eastern-Central Atlantic, so if the model keeps it by then, that would be discussed on Sunday. Last, I will issue my July 2009 Outlook, the following Sunday, June 28.

Weather456

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Watching A Few Areas but Overall Quiet

By: Weather456, 10:25 AM GMT on June 16, 2009

Broad upper ridging continues to ventilate convection along and to the east of a surface trough along 89W. A broad area of showers lies across the area from the Yucatan, Central America north of 13N and the Northwest Caribbean Sea. Last night’s QuikSCAT revealed sharp cyclonic turning along the trough with any possible circulation remaining over Honduras or a few miles offshore. Due this proximity to land, significant development of this feature is not expected during the next 24 hrs. This area is expected to move slowly westward enhancing moisture across the Yucatan region, which includes the Southern Gulf of Mexico. By day 2-3, the area is expected to move into the Bay of Campeche, enhancing moisture across Gulf Coast of Mexico and the Tabasco Plain. Conditions seem favorable enough for the continued monitoring of this feature but regardless of development, areas along the Yucatan could pick 1-2 inches with isolated 3 inches over the next three days. Additional rains are expected due to afternoon showers and a tropical wave moving through the area by Thursday.

A tropical wave is moving along 80W south of 18N at about 13 knots. This wave will probably help to enhance isolated-scattered showers across Jamaica and Caymans and Central America as it moves through the area today and early on Wednesday. However, the highest probability for heavy rains should remain west of those islands.

Interestingly enough a weak upper level trough is developing over the Eastern Caribbean, which is a day earlier than expected, and along with surface speed convergence (maybe associated with a weak tropical wave/surface trough) at the edge of the subtropical ridge, is enhancing clusters of showers and possible thunderstorms across the Eastern Caribbean Islands. This morning’s radar image showed almost all the islands receiving showers but as of 6:00 local time no rain has fall in Saint Kitts with ominous clouds approaching. This upper feature is expected dig further into the Central Caribbean over the next day and two with some showers will linger over the islands but the bulk shifting west across Puerto Rico and Hispaniola.

Models continue to forecast the development of a low pressure area offshore the Carolinas by Wednesday along the tail end of a frontal boundary. It is becoming unlikely that something subtropical or tropical may evolve despite favorable conditions due to the rapid northeast motion expected once offshore. I will continue to monitor the situation for any changes.

Other than those two areas, (Western Caribbean/Bay of Campeche and SW North Atlantic), I see no other signs of development through Friday.

Weather456



Precipitation Forecast for the next 24 hrs.


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Tropics Remain Quiet, Typical For June

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

Gulf of Mexico

The tropics remain quiet this morning, and little is expected over the next 48 hrs. The Gulf of Mexico remains high and dry under the influence of a dry northwesterly upper flow regime between a large upper high over Mexico and weakening upper low over the Yucatan. This upper low is expected to continue to weaken as it continues into Mexico, allowing upper ridging and its resultant stable flow to take over the Gulf of Mexico. Instability over Mexico will still allow moisture over the Bay of Campeche.

Caribbean

West-Central

The Caribbean remains much more moist than the Gulf of Mexico with upper divergent flow caused by an expanding ridge aided by low level convergence along a series of surface trough helping to generate a broad area of disorganize showers and isolated thunderstorms mainly over Central America. The chances of rainfall for the Western Caribbean sharply drops by weekend as the upper ridge (and the associated showers) shifts west to make way for the reintroduction of an upper trough which envelopes the area in upper confluent flow. In the meantime, lingering moisture will continue enhance the possibility of scattered showers over the area through mid-week.

A tropical wave is along 72W south of 17N moving west near 12 knots may seek to energize additional showers across the area over the next 3 days.

East

It seems, the upper level pattern will continue to maintain dry conditions across the Eastern Caribbean and little shower activity is expected through Tuesday.

Southwest North Atlantic

Models continue to show the development of a low pressure off the coast of the Carolinas through mid-week. While the system is expected to be non-tropical, initially, wind shear is expected to be extremely favorable and the NAVY NOGAPS and GFS are indicating the area will traverse the Gulf Stream and become a non frontal warm-core. Thus, a system similar to Tropical Depression One is not out of the question. However, I would like to see more models transition this feature to something tropical. Nevertheless, I will continue to monitor this feature.



Tropical Atlantic

A tropical wave is probably along the African coast near 16W-18W south of 15N, and is one of the more northerly waves of the season.

Some of the models are also developing a strong African Easterly Wave in the central Atlantic by next weekend but anything forming out there has to climb a mountain as high as Everest just to become something significant. A strong tropical wave is best monitored as it near the Antilles but that is almost 2 weeks away.



Weather456

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2004 Vs 2009; Tropical Update

By: Weather456, 11:11 AM GMT on June 14, 2009

Should 2004 be used as an analog year?

The rate of warming in the Equatorial Pacific during the spring of 2009 is roughly similar to the rate of warmer of two recent years – 2006 and 2004. El Nino is expected to develop during the summer months and the current trends, conditions and forecast mostly agree and most wonder will the El Nino have similar effects in 2006 where the conditions came quickly or 2004 where the conditions lagged. Today, I seek to compare the 2004 tropical atmosphere to that of 2009, in the case if El Nino conditions do lag.

El Nino Southern Oscillation

Probably everyone knows that a weak El Nino developed during 2004 and the degree of warming is similar to 2009 (with 2009 cooler) with the forecast calling for similar numbers. The uncertainty lies whether or not the conditions will lag similar to 2004.

North Atlantic Oscillation (NAO)


Both years experienced the positive phase of the NAO with mean sea level pressure higher than normal in both years for the Tropical Atlantic. However, 2004 anomalies covered the entire Atlantic while 2009 had below average pressures in the Caribbean and Gulf of Mexico. Another noticeable difference is that the index is expected to become negative during the summer of this year while in 2004 it remained positive throughout August and September, probably contributed the long-lived tracks of Frances and Ivan.

The above observations were reflected in the tradewind flow south of the subtropical ridge. Both years had striking similar tradewind flow but the trades ran about 5 meters per second higher in 2004. In addition, the subtropical ridge was found about 10-15 degrees more east in 2004, probably due to the classic positive NAO in that year and the weakening positive NAO in this year.

Sahel Rainfall

This factor would probably separate the 2 seasons. Though rainfall pattern along the ITCZ and over Sahel was similar in both years, 2009 is not expected to have such an active Cape Verde Season as 2004 did due to the below normal Sahel Rainfall and lower SSTs over the tropical Atlantic. However, because development is expected to be closer to home this year, a storm forming and tracking similar to Hurricanes Alex, Bonnie (TS), Charley, Gaston or Jeanne should not be out of the question.

Sea Surface Temperatures

On a sub-global scale, 2004 and 2009 had similar sea surface temperatures pattern but with noticeable synoptic and sub-synoptic scale differences. These differences and similarities are listed below.

Region 1 – Running above average for both years
Region 2 – Below to near normal for both years with 2009 having a greater area

Region 3 – Generally near normal for both years with sub-synoptic scale cool anomalous

Region 4 – Both had warm anomalies on either end of this region but 2004’s anomalies were greater and more widespread.

Region 5 – Both had anomalously warmer waters but 2009 anomalies were greater and more widespread. I find this rather contradicting the quiet Cape Verde Season theory but if the tropical Atlantic remains cooler than normal then that remains the case.



Steering Flow

Three of the four strongest storms of 2004, travelled on almost a steady west-north-west to northwest motion, with little recurvature before the reached land. 2009 may present a similiar situation but north of 20N (region 2 above). The lastest CFS model run shows a favorable pattern for random development in that region of the Atlantic, placing the East Coast at 50/50 risk this year as oppose to the Caribbean, Florida and Gulf Coast in 2004. However, the Caribbean and Gulf still remain areas of concern this year mainly due to the fact that more development seems to take off closer to home.

Conclusion

It is clear that the general atmosphere of 2004 and 2009 was similar but should not be entirely used as analog years since both had important sub-synoptic differences in sea surface temperatures and Sahel Rainfall. In addition, despite both potentially having weak-moderate warm episodes we still are uncertain as to the effects this year’s El Nino so caution must be taken when comparing this year to 2004.

Tropical Update



Upper level systems seem to be the predominant weather holders across the tropical Atlantic this morning. First, a large upper ridge is stationed over the heart of Mexico, providing deep layer blocking and anticyclonic flow over the South-Central United States. This upper high is referred to as the North American Monsoon Ridge and its cousins are the Bolivian ridge of the South American Monsoon and the Tibetan Ridge of the Asian Monsoon. Meanwhile, a cut off upper low is situated right along the Yucatan Peninsula coast and the confluent flow between the two features is maintaining a dry stable airmass across the Gulf of Mexico.

Over the Caribbean, a surface trough is along 85W and the divergent flow east of the upper low, also being enhanced by a ridge over the Eastern Caribbean, is generating numerous cloudiness, showers and thunderstorms over the Caribbean from central America to the Greater Antilles which includes, Jamaica, the Caymans, Cuba and Hispaniola.

A tropical wave is along 68W south of 18N moving off towards the west near 10-15 knots. This tropical wave is less convective than 24 hrs ago when it brought a good amount of beneficial rains to the Southern Antilles which has been drier than normal due the lack of the ITCZ influence which remains south of 5N.

The forecast calls for the upper low to slowly move west into the Yucatan over the next 24 hrs. Due the blocking nature of the ridge over Mexico, the upper low will linger through day 2 while becoming less defined and by day 3-4 will dissipate. During this time, the surface trough will remain over the region and thus the chances of showers seem to shift west across the Yucatan, Western Cuba, the Caymans and maybe even the Florida Keys and Bahamas. The tropical wave along 68W will pass through the central Caribbean over the next 24 hrs, probably enhancing showers over Hispaniola. Lingering debris moisture is expected elsewhere.

Most of reliable global models continue to forecast the development of a low pressure area along the tail end of a frontal boundary offshore N&S Carolina Tuesday/Wednesday and while sources maybe non-tropical there are some indications that this feature may have enough time to become subtropical. Whatever forms is expected to initially move east, or slightly south thereof, but eventually move off towards the northeast. The environment in that area is forecast to become marginally favorable so the area will be watched but only the UKMET, CMC and NOGAPS showed transitions to a non frontal feature, as the GFS quickly takes it out to sea as a frontal system. Nevertheless, I will monitor the area.

Elsewhere, there are no other areas of interest. The tropical wave in the east Atlantic likely fell apart due the differences in the oceanic environment.


TRMM 7 day rainfall accumulation ending 14 June 0300 UTC. A combinations of the upward pulse in the Madden-Julian Oscillation, upper level divergence/forcing, a series of troughs and tropical waves and meso-scale convective systems conspire together to bring wet conditions to the region over the past week.

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Western-Central Caribbean soaked by upper level systems

By: Weather456, 10:44 AM GMT on June 12, 2009

Western Caribbean

A sharp upper trough continues to linger across the region from the Southwest Atlantic into the Western Caribbean producing numerous showers and thunderstorms in a diffluent zone to its east over Hispaniola, Jamaica, Eastern Cuba and the southern Bahamas. Meanwhile, a less convective surface trough remains along 80W. Over the past 24 hrs, the upper trough has amplified with two concentrated upper circulations over the Bahamas and South of Jamaica. Over the next 24-48 hrs, the trough is expected to continue to split with the northern portion moving off into the Atlantic, leaving the southern extension in the Caribbean. The latter is expected to slowly move towards the west through day 3 and coupled with the surface trough, favors the development of continued moisture over the weekend.

Upper winds remain unfavorable for any development of these features over the next 24hrs. Similarly, the models have been very inconsistent with developing a feature over the Western Caribbean and currently the feature is forecast to remain an open trough. Since vertical shear has been dropping and will continue to drop, I will monitor the region for any signs of change but currently I’m not expecting anything significant but rain, which some places could see 3 inches of. This increases the likelihood of flooding in some locals over the Haitian Peninsula and eastern Cuba.

Depiction of upper and surface features over the Western-Central Caribbean



Central Atlantic

A tropical wave along 55W will be reaching our neck of the woods (Lesser Antilles) by tomorrow bringing with it a modest increase in moisture mainly over the southern Antilles.

24 hr rainfall accumulation (mm) valid through Monday



Eastern Atlantic

I know it’s too early to look out here, but one of the more impressive wave of the season is currently rolling off African with this morning’s satellite imagery showing deep convection along the axis. Development is not expected.



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Heavy Showers Continue Over Western-Central Caribbean

By: Weather456, 10:43 AM GMT on June 11, 2009



Western Caribbean

A persistent upper trough extending from the southwest North Atlantic into the Caribbean continues provide upper diffluent flow along a broad surface trough of low pressure that exists near 75W. Heavy thunderstorm activity is found along this trough between 80W-70W, with the largest cluster south of Hispaniola. Currently, there are signs that this surface trough is trying to become more amplified in response to the upper level forcing. However, development of this feature is not expected over the next 24-48 hrs due to strong vertical wind shear.

The current forecast calls for the southern extension of this upper trough to seclude and track west into Central America through 3-5 days. Meanwhile, the surface trough is expected to move towards the northwest and coupled with the cut-off low, favors the continuation of deep layer moisture across the Western Caribbean over the next couple of days.

Much of the global models continue to hint that a weak surface low may develop along the trough and track over the Western Caribbean, reaching the Yucatan Channel by Sunday. The GFS has dropped the system all together, but this model is doing the poorest in handling the situation. The ECMWF solution allows for a more gradual development with the low not reaching the northwest Caribbean by Monday/Tuesday. At 72 hrs, the upper low has not entirely left the region and remains over Central America causing modest shear over the Northwest Caribbean. At 120 hrs, the upper low is well into the Eastern Pacific, allowing for a greater area of low shear and ventilation for any possible cyclone. Currently, the feature remains quasi-stationary over the Central Caribbean and thus the ECMWF seems to have the most reasonable solution, with the surface trough gradually moving northwestward over the next 3-5 days, and has the potential to develop into a disturbance.

Regardless of development, deep layer moisture will continue to spread across the Western Caribbean region over the next 3-5 days, with the highest probability over Jamaica, Eastern Cuba, Haiti and the Bahamas.

Elsewhere

A tropical wave along 51W south of 13N moving west near 10-15 knots will reach the Eastern Caribbean Islands by Saturday, bringing with it cloudiness and showers, especially over the Windward Islands and Trinidad. The environment over the northeast Caribbean is not expected to enhance much instability along the wave axis thus a lower probability of rainfall there.

Probability of rainfall totals exceeding 24 mm (about 1 inch) over the next 3 days.



Tropical Wave Train as of 00Z June 11, 2009



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Tropical Update

By: Weather456, 10:49 AM GMT on June 10, 2009

Water vapor satellite imagery this morning showed an upper trough continues to persist from east of Florida to the Western Caribbean, and while the upper trough appears less of a predominant weather maker as it did over the past day or two, it continues to produce scattered showers and thunderstorms within a diffluent zone extending from Honduras/Nicaragua, across Jamaica, Central-Eastern Cuba, Hispaniola, the Bahamas and into the southwest North Atlantic.

Meanwhile, a tropical wave is along 79W, south of 20N moving west near 14 knots. This wave does not appear to have much weather with it over the Caribbean Sea but is enhancing strong clusters of thunderstorms along northeast South America, especially over Colombia.

This upper trough is expected to remain in place over the region for the next 2-3 days and with the enhancement of the aforementioned tropical wave, favors the development of scattered showers across the region. By weekend, models are suggesting that the trough will split and a cut-off upper low will develop over the Western Caribbean and shift west into the Yucatan by Monday.

Most of the global models continue to hint, the development of a weak surface low somewhere in the Western Caribbean, preferably the southwest Caribbean (due the strong vorticity at the present) along the tropical wave. The four models; GFS, NAM, ECMWF and NOGAPS continue to suggest that a closed low pressure area may develop over the southwest Caribbean and track northwestward. Wind shear currently remains unfavorable for development due the upper trough to the west but as the cut-off low forms and tracks west, a region of low shear may develop over the northwest Caribbean in about 3-5 days. This creates a shear pattern that is not reasonable with the GFS, NAM and NOGAPs solutions but complies with the ECMWF which develops a closed low through 3-5 days.

The development of a possible tropical cyclone within the next 48 hrs appears low due to the lack of reliable model support and unfavorable upper level winds, but I will continue to monitor the area for any signs of changes.

Regardless of development, the upper level environment across the region will maintain an unstable airmass across the Western Caribbean over the next 2-3 days.

72 Hr Rainfall Accumulation; Valid 2 AM Saturday



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Tropical Wave to bring additional rains to the Western Caribbean

By: Weather456, 10:37 AM GMT on June 09, 2009

Caribbean

A slow moving upper trough continues to linger roughly west of 80W and this persistent feature continues to enhance scattered convection across Southern Central America, Jamaica, Cuba, the Caymans, Hispaniola and the Bahamas. Over the next 2-3 days, a westward moving tropical wave currently near 71-72W will enter the region and upper divergence ahead of the upper trough and a possible cut-off upper low will interact with the tropical wave causing additional showers and thunderstorms across the area. The GFS has been hinting that this divergence favors the amplification of the tropical wave and results in a weak stationary low south of Jamaica and this solution is becoming more likely as indicated by the Tropical Prediction Center.

Now here we must differentiate between the development of a weak surface low and the development of a tropical cyclone. While all of the global models show some low level vorticity in the West Caribbean in 3 days, only two of the models develop a closed low – ECMWF and GFS. The development of the surface low is rather a feedback to the upper level forcing and with the uncertainty as to the shear forecast; development is not guaranteed at this point.

What is somewhat guaranteed, is that deep layer moisture will spread north across Jamaica and Eastern Cuba over the upcoming week. Total amounts may exceed 1-2 inches with lesser amounts in the Caymans due their relative position to the features. By weekend, the moisture seems to make its way up near the Bahamas.

I will continue to monitor the area for any signs of further changes.

Southwest North Atlantic

A similar pattern exists over the Southwest North Atlantic where upper divergence is spreading moisture ahead of the northern extension of the upper trough that is over the Western Caribbean. There is some potential for a surface trough to develop over the area as the upper level feature track northeast-east northeast over the upcoming days but conditions are only expected to become marginally favorable for development. The area will be monitored but has less than 15% of becoming something significant.

This week’s accumulated rainfall thus far:





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Development Uncertain; Rain Likely

By: Weather456, 10:40 AM GMT on June 08, 2009

Synoptic Overview of the Caribbean depicting several features - green arrows show potential moisture surge.



A sharp upper trough has its axis extending from 31N-77W to 14N-90W right along the coast of Guatemala. Large scale diffluent flow east of this feature continues to generate a broad area of cloudiness and showers across the southwest Atlantic, Bahamas, Cuba and the Western Caribbean waters. The most intense convection continues to lie within the southwest Caribbean in association with a broad area of low pressure.

This morning’s satellite imagery showed a burst of heavy intense convection in and around the area of low pressure with most of the heavy thunderstorms remaining offshore Central America. As of 0900Z (5 am EDT) this morning there appears to be little surface reflection and available surface observations did not indicate falling pressures or cyclonic wind shifts that may suggest a surface trough. Current wind shear remains unfavorable for anything much to develop over the next 24-48 hrs. However, by mid-week, there are number of factors which suggest the area should still be watch. A tropical wave currently in the Eastern Caribbean is expected to reach the Western Caribbean by Wednesday. If diffluent flow aloft remains persistent, a surface reflection in the form of a trough may develop across the area. If shear continues to decrease as it did over the past days, the interaction between the two features (tropical wave and surface trough) may initiate a weak surface low. This scenario is not guaranteed and depends mainly on wind shear. Only two reliable models continue to forecast development so it remains a 30% chance for now.

Regardless of development, rains will continue across Central America and is expected to extend northward through mid-later this week across Jamaica, the Caymans, Cuba and possibly Haiti. Thereafter, the rains may reach the Florida Peninsula or Bahamas by weekend.

Estimated rainfall accumulation (in) through Saturday



I will continue to monitor for any signs of changes.

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Tropical Update

By: Weather456, 12:49 PM GMT on June 07, 2009




There is a lot to take about today in the tropics. Firstly, the upper trough that was stationed along Florida and the Eastern Seaboard yesterday has dug into the Caribbean and over Central America as expected. The diffluent flow ahead of the trough continues to initiate and spread scattered cloudiness and showers from a broad area of low pressure in the SW Caribbean across Central America and the Northwest Caribbean which includes the eastern Caymans, Jamaica, Cuba, Hispaniola and the Bahamas. This diffluent zone reaches as far as the Eastern Seaboard and Bermuda. This upper trough is expected to linger across the region through Tuesday and probably continue to enhanced showers and thunderstorms across the Western Caribbean. By Wednesday, a tropical wave near 60W will enter the region and interact with the trough maintaining additional moisture across the region. During this time, a surface trough is expected to develop over Central America and with the introduction of the wave near 61W the area will be monitored for development since there is some indications that vertical shear is currently decreasing. However, I can say, development does not seem likely over the next 48 hrs due to the proximity to the Central American coast, the fact that the area is not showing any signs of development and uncertainty with vertical shear associated with the upper trough. Only two of the three models that develop this feature remains reliable – GFS and ECMWF. Regardless of development, this area is expected to drift northward with a westward bias and continue to maintain moisture across the area.

A tropical wave is near 61W south of 20N moving towards the west near 14 knots. At its north and south ends of the axis, the wave is entering a diffluent zone resulting in scattered showers and isolated thunderstorms across Trinidad and northeast Venezuela and the northeast Caribbean. Piarco, Trinidad And Tobago had light rain showers this morning and as a type, we are getting a moderate shower here in Saint Kitts. The wave is expected to continue west, spreading moisture across Puerto Rico and Hispaniola over the next day or two.

To the north of the tropical wave, a mid-upper level low is spinning near 24N-55W and typically, as many know; its surface reflection is a surface trough attached to the tropical wave. This morning’s satellite imagery showed an increase in shower activity along the trough and two the east of the upper low. This upper low will continue to linger over the region through Tuesday but begin to lift out by Wednesday as the subtropical jet lifts north and east from the Caribbean. Shear is expected to relax at the center of the low and coupled with warm enough SSTs the area will be monitored even though it has a slim chance.

Severe weather struck southern Florida on Friday causing strong thunderstorms and heavy rainstorms that brought gusty winds, hail and heavy rains across some counties. Below is a YouTube video of one of the severe thunderstorms that brought 80 mph wind gusts and heavy rains to the Miami area. Courtesy Weatherundeground blogger, hurricane23. Considerable showers and thunderstorms were expected to persist over Florida, but water vapor imagery show a region of dry air moving into the area, the probability may become lower.



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Tropical Update

By: Weather456, 11:40 AM GMT on June 06, 2009



Gulf of Mexico, Southeastern United States and Southwest Atlantic

A deep layer low pressure area is currently a spinning along the western Coast of Florida and coupled with a surface frontal system is producing scattered showers and thunderstorms from the Northwest Caribbean to along the US East Coast which includes, Cuba, the Bahamas and Florida Peninsula. This system is estimated to have dropped 2-3 inches across the Southeast United States and even though it is forecast to pull northeast along the Eastern Seaboard, moisture is expected to linger across Florida. Due the slow movement of this trough, the GFS thinks this will linger long enough to dig further south and probably contribute to the northward pull of potential tropical development in the Western Caribbean.



Caribbean

A tropical wave near 58W south of 20N is expected to enter the Eastern Caribbean during the next 24 hrs bringing with it moisture for the islands with the heaviest rains probably where the environment is most unstable over Trinidad, Venezuela and the Windwards. They are expected to get up to 1 inch while others less than an inch. The moisture is expected to spread to further east across the Virgin Islands and Puerto Rico later on Sunday and Monday.

The main story remains the broad area of low pressure over the Southwest Caribbean and Eastern pacific, centered on a 1010 mb low just to the west of Costa Rica. Much of the global models continue to forecast this feature to pull north over Central America along a surface trough of low pressure and emerges over the NW Caribbean in 3 days where development occurs under somewhat favorable conditions. While a cause of development is becoming clearer, the forecast motion continues to remain highly uncertain. The deep layer steering is pulling it northeastward due the upper trough and break down of the ridge while the shallow layer steering has a stronger surface ridge and shallower upper trough causing a more westward track. It does not seem we will fully understand where the system will go until it develops but the model consensus is for it to move towards the north, and areas like the Caymans, Jamaica and Cuba could be affected regardless of motion.

Currently, a broad area of disorganize showers continue to produce showers over Central America with places already receiving an inch of rain over the past 24 hrs. Over 3 inches of rain expected over the next week regardless of development across the mentioned areas and Haiti and some places could get over 10 inches by next Saturday if the storm do materialize.

As I mentioned in the previous blog, until we get the surface disturbance in the Northwest Caribbean development remains uncertain (30%) but the situation should and will be monitored since the conditions are there to allow genesis.

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Rains Over Southeastern USA; Watching the SW Caribbean

By: Weather456, 10:22 AM GMT on June 05, 2009




South Eastern United States

The frontal system forecasted yesterday is currently moving across the Southeastern United States spreading moisture from Florida to the Mid-Atlantic States. Radar estimated that up to 3 inches of rain fell across the area in the past 24 hrs. This area is expected to continue northeastward along the Eastern Sea board and continue to dump up to an inch of rain along the East Coast. Flood watches and warnings have been posted for parts of the affect area. The inflow off the Gulf of Mexico may help enhance afternoon thunderstorms over the Florida Peninsula.




Watching the SW Caribbean

A broad area of low pressure in association with a vigorous monsoon trough extends across the Eastern Pacific, Panama/Costa Rica and the southwest Caribbean Sea. Satellite imagery and QuikSCAT show a classic monsoon flow with thunderstorms embedded south of the trough in the monsoon southwesterlies. Vertical wind shear remains unfavorable at the moment and development is not expected for the next 24 hrs.

However, most of the reliable computer models (GFS, UKMET, NOGAPS and ECMWF) continue to develop a broad area of low pressure in the Southwest Caribbean along a surface trough as early as Sunday (48 hrs) and takes it either over Central America or in close proximity. The area then reaches the Northwest Caribbean on Tuesday where vertical shear is expected to relax, coupled with the warm sea surface temperature and possible introduction of a tropical wave, it is forecast to strengthen. By next Friday, the GFS is forecasting a hurricane to impact Southeastern Cuba which I think is a little overdone for several reasons: land interaction with Central America will potentially slow or hinder cyclogenesis until the area reaches the Northwest Caribbean and some models weaken shear to a greater extent than others (due to the upper trough) with the majority showing shear over a distant to support only a tropical storm. I feel that the CMC is understating it based on the consensus that shear will weaken. It seems the ECMWF and NOGAPs has the best solutions in terms of intensity.

It is still too early to say where this potential system may go if it develops. The consensus for the short-term (within 1 week) has it interacting with Honduras/Nicaragua, then moving north across the Caymans and then impacting Cuba in 1 week. The system is ultimately being steered towards the north-northeast in the deep layer flow ahead of an upper trough that is expected across the Eastern Gulf/Extreme Northwest Atlantic. Beyond 1 week, it seems the models are hinting that the subtropical surface ridge may help turn it more westward once it leaves Cuba over the Central-Western Bahamas and the east coast of Florida. The system is pulling northeast offshore the US East Coast ahead of the advancing trough at the end of the forecast cycle.

There is still the uncertainty of development and track right now and a lot can change over the upcoming days as this could occur in the Eastern Pacific all together so the best we can do is monitor the situation for now and not be over concerned. What I can say is the models are forecasting favorable conditions for cyclogenesis, but whether or not this feature takes off is unknown. I’ll give it a 30% chance for now.

Regardless of development, moisture is expected to spread across Central America, the Caymans, Jamaica, and Cuba and to a lesser extent Haiti, later next week.

Surface Forecast for Kingston Jamaica



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Tropical Update

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



Gulf of Mexico

Broad mid-upper flow centered over Southern Louisiana continues to maintain scattered showers across the Southeastern United States, Eastern Gulf of Mexico and the Yucatan Peninsula. This feature is expected to develop as part of a frontal feature and shift northeastward across the Southeastern United States. Up to 2 inches of rain could fall along the US Gulf coast, Southeastern United States and Florida over the next day or two as the system moves across the area.

Tracking Possible Development Next Week

Most of the major global models (GFS, ECMWF and NOGAPS) continue to forecast development in the Western Caribbean next week. Genesis appears to begin in the Southwest Caribbean as a weak low pressure area develops over the area by Sunday and moves towards the northwest by Monday. During this time, a sharp upper trough digs across the region generating a deep moisture field across the Caribbean and further enhancing low level vorticity along this feature. This upper trough feature comprises the subtropical jet and begins to lift by Tuesday, allowing for a favorable upper level pattern to develop and the low pressure intensifies over the warm waters of the Western Caribbean. During genesis, a tropical wave, currently located in the Central Atlantic is introduced and it is uncertain how it will contribute to the development of this feature.

Though, environmental conditions appear only somewhat favorable for development. Wind shear is forecast to decrease but it seems much of the convection remains east of the center indicating some southwesterly shear from the upper trough. Both the GFS and CFS show this occurring during the next MJO upward pulse, there seems to be some model consensus and the time frames and solutions are feasible. I’ll give it a 30% chance of occurring for now. The models did pretty well within 1 week for 90L and Tropical Depression One.

Regardless of development, a deep moisture surge can be expected across the Central-Western Caribbean from Central America to Cuba, including Jamaica and the Caymans. I will continue to monitor the situation as it is subject to change as we get closer.

Tropical Invest 92L

Invest 92L is gone and current satellite imagery and surface observation still show some weak reflection as it continues to weaken and eventually dissipate or be absorbed into a larger low pressure area.

There is still some debate over whether 92L was a subtropical storm or not at its peak on June 2. The system had clusters of organize deep convection near its center of circulation with the highest winds, 45 knots, also found near its center. Subtropical numbers from the Satellite Service Division peaked at ST 3.0 (45 knots) yesterday which is derived from analyzing subtropical cloud patterns seen on satellite imagery. Finally, probably the most striking peace of evidence was the warm-core seen on microwave imagery from AMSU, which indicated tropical characteristics. Here we clearly see a subtropical storm but Invest 92L was moving over waters near 16C and the NHC states average sea surface temperature that helps lead to subtropical cyclogenesis is 24C (75F). In every tropical weather outlook they stressed the point of the sea surface temperatures and was probably the likely cause for the lack of classification.

Image taken by MODIS AQUA 3 June 1440 UTC or 1040 EDT of Subtropical Invest 92L



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Invest 92L; Heavy Rains for Gulf Coast

By: Weather456, 10:44 AM GMT on June 03, 2009

Invest 92L

Invest 92L is located near 45N-25.5W moving quasi-stationary. Estimated surface winds are near 35 knots with a minimum central pressure near 1000 millibars. This morning satellite imagery showed a well-define circulation but with little associated deep convection. There is evidence of slight weakening as the winds have dropped, pressure has risen and ST numbers are down from 3.0 to 2.5. The disturbance is moving within a weak steering environment due to the upper trough it is embedded within, but should start moving towards the east over the next 24-48 hrs. Despite low vertical shear, the system continues to move over 16-18C waters and will likely weaken as it heads east. The storm will continued be monitored until then.

There is still some debate over whether 92L was a subtropical storm or not yesterday, June 2. The system had clusters of organize deep convection near its center of circulation with the highest winds, 45 knots, also found near its center. Subtropical numbers from the Satellite Service Division peaked at ST 3.0 (45 knots) yesterday which is derived from analyzing subtropical cloud patterns seen on satellite imagery. Finally, probably the most striking peace of evidence was the warm-core seen on microwave imagery from AMSU, which indicated tropical characteristics. Here we clearly see a subtropical storm but Invest 92L was moving over waters near 16C and the NHC states average sea surface temperature that helps lead to subtropical cyclogenesis is 24C (75F). In every tropical weather outlook they stressed the point of the sea surface temperatures and was probably the likely cause for the lack of classification.



Gulf of Mexico

Broad mid-upper level flow covers the central Gulf of Mexico and is helping to generate scattered showers and thunderstorms across the region. While there has been evidence of some surface reflection south of Louisiana over the past 12 hrs this system remains in an environment unfavorable for tropical cyclogenesis. In addition the models show this system developing as a non tropical entity along the US Gulf Coast and moving northeast across the SE United States. The area will continue to be monitored. Regardless of development, heavy rains are expected over the northern Gulf coast from central Louisiana to the Florida Panhandle.



Elsewhere

Much of the global models continue to show enhanced vorticity over the SW Caribbean over the upcoming days and the GFS, NOGAPS and ECMWF develop a low pressure area somewhere in the Western Caribbean between 3-6 days. Despite the models having an inconsistent date and point of formation, vertical shear is expected to be favorable in that part of region. The ECMWF has the strongest solution around the next MJO upward pulse. This will be monitored.

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Tropical Update; Non-Tropical Invest 92L

By: Weather456, 10:32 AM GMT on June 02, 2009

Our thoughts and prayers goes out to the families and love ones of those lost in yesterday's crash of Air France Flight 447.

A broad upper ridge has its axis extending from the Eastern Pacific to the Gulf of Honduras with large-scale anticyclonic flow generating and advecting numerous scattered showers across the Yucatan Peninsula, Gulf of Mexico, Northwestern Caribbean and the extreme southwest North Atlantic. Satellite imagery supported by vorticity maps at CIMSS revealed a low level reflection in the form a surface trough over the Eastern Bay of Campeche. Development of this feature remains unlikely due to the unfavorable upper level environment in place for the next several days. The area will be monitored. Regardless of development, showers with isolated thunderstorms can be expected across that region over the next 24 hrs.



Non-Tropical Invest 92L

A non tropical area of low pressure is located north of the Azores Islands at 42.1N-23.5W, moving off towards the north-northeast near 11 knots based on satellite imagery. QuikSCAT and surface observations indicated wind nears 35 knots and an estimated central pressure of 1000 millibars. This system possess both tropical and non-tropical characteristics with satellite imagery showing clusters of convection and gale force winds in and around the low pressure area, implying tropical. On the other hand, the system possess a flat thermal core in the lower levels and embedded with a large cold core low, implying non-tropical. These factors constitute a subtropical cyclone, and if a low level warm-core structure becomes more evident, it has potential to become a named storm.

Future intensity remains uncertain as the low pressure area moves off towards the north. The system has 5-10 knots of shear in its favor but moving over waters near 18C! There are processes to explain how these types of low can produce convection over such cold waters. Conditional Instability of the Second Kind (CISK) is one factor and in this case convection is maintained by strong latent and sensible heat fluxes resulting from a large difference between air and sea surface temperature.

There are no other areas of interest but some of the models are indicating a weak low pressure to develop over the SW Caribbean over the upcoming days.



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June Outlook

By: Weather456, 11:15 AM GMT on June 01, 2009

Hurricane Season 2009 begins today and we can expect a near to slightly average season due to various factors with the development of El Nino potentially being the biggest implication. In my 2009 Hurricane Season Outlook issued in mid-May, I expect 12-14 named storms, 6-7 hurricanes and 3 major hurricanes with a less active Cape Verde Season than previous years and development closer to home, preferably west of 50W and north of 20N, in the case with Tropical Depression One.

2009 Hurricane Season Names



June Climatology

June normally sees three tropical cyclones per 5 years, that is, over a five year span; we see three tropical cyclones forming in June. However, over the past six years we have seen 5 tropical cyclones forming in June indicating some exceptions. This is the time of the year when sea surface temperatures and instability increases across the tropics. The mid-latitude retreats and become less active allowing a more favorable environment for tropical cyclone formation.

In June, we typically look at the Western Caribbean and Gulf of Mexico for development, as conditions are ripe for tropical cyclone formation. We have warm sea surface temperatures, ample moisture and heat, topped off with an overhead ridge allowing favorable shear. Westerlies remain over the Tropical Atlantic which makes it difficult for systems to form out there.

Any system forming here, normally tracks northward or northeastward, these are very consistent paths, especially the tracks observed over the past six years.


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

General June Outlook

The most preferable time for cyclogenesis this month, seems to be in the Western Caribbean during the latter two weeks or nearing the end of June. The Madden Julian Oscillation (MJO) is the prime intraseasonal indicator of tropical cyclogenesis and two of the three major models show its upward pulse from 15 June to 10 July. During this time, there are indications that the subtropical jet will lift northward allowing weak vertical shear to persist over the tropical Atlantic and most importantly, the climatological favored areas for the month.

Detailed June Outlook

Sea Surface Temperatures

Sea surface temperatures have warmed considerable over the past week and even though they remain lower than previous years, are comparable to 2008 and 2004. The most noticeable warming occurred in the Gulf of Mexico and the western edge of the Main Development Region (MDR). The latest North Atlantic Oscillation (NAO) figures showed the positive phase we saw in April-May has weakened over the past 2 weeks, likely contributing to a weaker subtropical ridge and lighter trades. The NAO is forecast to continue to transition to negative as we progress into June likely contributing to additional warming of the MDR. However, cool anomalies continue over the SW Atlantic where frontal/mid latitude synoptic weather dominated for the past 2-3 weeks and eastern end of the MDR, where African dust has been prevalent.


Figure 2: Operational SST Anomaly Charts (C) for May 28 2009 from NOAA/NESDIS. Notice the warm anomalies in the Western tropical Atlantic and Western Caribbean/Gulf and cool anomalies over the SW Caribbean and Eastern tropical Atlantic.

Vertical Wind Shear

Vertical wind shear have been higher than normal for regions roughly south of 20N and this due to the southern extent of the subtropical jet. The subtropical jet is the likely cause because regions north of 25N have been experiencing lower than normal vertical wind shear. This likely contributed to the formation of Tropical Depression One. This pattern is reminiscent of El Nino years, but, I’m not too quick to incline that is the cause thus yet since it is not expected to be a persistent pattern. The subtropical jet is expected to lift over the next 2 weeks allowing weak vertical shear to persist over the tropical Atlantic and most importantly, the climatological favored areas for the month.


Figure 3: Shear anomaly for June 01 2009, which was basically the pattern over the past 2 weeks showing above normal vertical shear for regions south of 25N, wehere the subtropical jet lies and low shear in the region between the subtropical jet and polar jet.


Figure 4: 18Z 31 May GFS wind shear long-range forecast showing low vertical shear and the position of the subtropical jet through mid-June 2009.

Enhanced Rainfall

Most of the models agree that the Madden Julian Oscillation will suppress tropical rainfall during the first 1-2 weeks of June but there is the increasing likelihood that the upward pulse will return to the Atlantic during the latter half of June. Tropical cyclogenesis is typically favored in the upward pulse and suppress in the downward motion. However, tropical cyclogenesis may or may not occur in either phase.

Sahel Rainfall/Dust

Over the past month Sahel rainfall has been wetter than normal in the west near the coast but drier than normal further east inland. Drier than normal African rainfall tends to increase the concentration of dust over West Africa but conversely lowers the frequency of tropical waves. As we saw yesterday, this may ultimately lead to less frequent but strong outbreaks of Saharan Dust over the tropical Atlantic, and possibly further reducing SSTs there.


Figure 5: May rainfall anomaly for Sahel shwowing wetter than normal precipitation for Western Sahel and drier conditions for Eastern Sahel. Eastern Sahel is where the dust and tropical waves form.

Steering Flow

The forecasted mean sea level pressure for June shows a sprawling moderate in strength subtropical ridge over the Eastern Atlantic. Coupled with the 200 mb flow (not shown), storms forming the Caribbean will tend to travel west to northwest; storms forming in the MDR (which is unlikely) will tend to move towards the west; and storms forming north of 25N will tend to move northwest with re-curvature more possible.


Figure 6: Mean Sea Level Pressure for June 2009 showing a large sprawling Subtropical Ridge.

Summary

There is a 30-40 % chance of development of a tropical system during 1-15 June and 40-50% chance during 16-30 June; with a 75% chance of it originating in the Western Caribbean/Gulf of Mexico, a 20% chance in the Eastern Caribbean/SW Atlantic, a 5% chance in the tropical Atlantic.

Tropical Update

A band of showers extends from the Yucatan Peninsula, northeastward across Cuba, the Bahamas and the SW Atlantic associated with a shear line ( a frontal boundary that disintegrated into a surface trough). That is the only area of convective activity in the Atlantic today.

While checking some the models this morning, they were showing increase low level vorticity in the SW Caribbean and this maybe associated with the ehancement of the Colombian low by a tropical wave moving over Eastern South America as we speak. Several models including the 06Z GFS, ECMWF and CMC develop a low pressure area over the area over the upcoming days. Vertical shear is expected to drop to 10 knots over that part of the Caribbean later this week so the area will be monitored. This has a 20% chance of development and even lower chance of surviving if shear remains unfavorable to its north.

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

Weather456's Tropical Weather Blog

About Weather456

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