MyFoxHurricane.com blog

Eastern Atlantic waves bear watching

Posted by Andy Johnson under Daily updates

Two tropical waves in the eastern Atlantic appear to be merging into one system. Both of the waves are south of the very strong Saharan Air Layer (SAL) that has caused dry dusty air over much of the eastern Atlantic north of 15°. Convection has increased today, although NHC has stopped running models on this system, at least for now. Once a new center is identified after some contraction, NHC will likely start running new models, perhaps by Sunday afternoon. Shear is relatively low near the combined wave and is forecast to be low for the next few days. Long range models such as the GFS eventually show a threat from the wave to the northern Leeward Islands as a tropical storm. The long range models have great uncertainty but the 18Z GFS run today (July 31) shows a tropical cyclone threat to the east coast of Florida by the end of next weekend. In addition, the large convective cluster that is inland over Africa and will be exiting into the Atlantic over the next day or so poses a threat for development, also. The 18Z GFS run shows a potential tropical cyclone in the mid-Atlantic by next weekend with a potential  threat to the Lesser Antilles.

Another wave in the central Caribbean is interacting with a TUTT low just to its west. The moderate shear over the wave will relax by Monday but by then the wave will be approaching Central America. At that point in time, the wave will likely be too close to land to develop.

I have circled the 3 waves in the enhanced satellite image below.

The enhanced GOES image below shows the position of the  TUTT low to the location of the tropical wave to its west. The upper low is causing moderate shear over the wave at the present time.

The Saharan Air Layer (SAL) shown in the image below in orange and red tints remains strong much of the eastern Atlantic but is just far enough north (of 15°) to not have any major dampening effect on the merged tropical wave centered closer to 8° N.

The graphic below is the 228 hr forecast plot from the 18Z GFS model on July 31, 2010. The models are subject to large errors in intensity and location at this time range. However, the model is currently showing a potential threat to the east coast of Florida by the merged wave currently in the central Atlantic by next weekend. It also shows another potential tropical cyclone developing from the convective cluster currently over the Sahel region of Africa.

Invest 90L slow to form

Posted by Sheena Parveen under Daily updates

Invest 90L may soon interact with a larger tropical wave to its East.  The interaction will add increased moisture and instability to the system, and some models are developing it much further by late next week.  As for now, the two tropical waves are unorganized, with shower and thunderstorm activity scattered throughout.  As of 8am Saturday, this system was about 800 miles SW of the Cape Verde Islands.

Computer models continue tracking it West, some pushing it North of the Caribbean Sea, and some pushing it into the Caribbean Sea.  At this time, it’s too far out to tell, so keep checking back for updates.

Wind shear is forecast to remain moderate around the Lesser Antilles over the next few days, but current wind shear is relatively low over Invest 90L.  Slow development of this system may be expected into next week.

Elsewhere, we are watching another tropical wave, extremely unorganized at this time, continuing to travel West through some higher wind shear in the Caribbean. 

90L still disorganized, may develop next week.

Posted by Dave Osterberg under Daily updates

As of 5AM Friday morning, invest 90L was still very disorganized. By looking at the satellite, there are a few clusters of thunderstorms, but nothing to indicate any real organization. The Hurrican Center gives this system a low chance for organization over the next 48 hours. Some people have asked me about this map. The low, medium, or high chance for development is only in the next 48 hours. It does not indicate what may happen 5 days down the road. Speaking of down the road, many computer models do develop this in the long term. At this point, the computer models should be taken with a grain of salt. Bottom line, if you don’t have a certain fix on where the center is,  you can’t get a real good idea of exactly where it’s going. You can get a general idea, but not certain. So 90L could easily head north of the islands, and it could easily head south.  A look at a few of the computer models will tell us this story. The CMC, and the HWRF both develop this system, and the HWRF makes it a hurricane well north of the islands. But on the other hand, the European and Navy NOGAPS models take this system into the Caribbean. This difference of opinions is common with an invest, and I encourage everyone to keep checking back throughout the next week. Have a great weekend.

Invest 90L forms in Atlantic

Posted by Sheena Parveen under Daily updates

An area of disturbed weather, known as Invest 90L, was about 600 miles SW of the Cape Verde Islands as of 2pm Thursday.  This broad area of low pressure is moving West/NW and is unorganized at the moment with scattered thunderstorms.

Satellite imagery shows the continued un-organization of this system with no defined cyclonic flow, but some models are holding on to it into next week.

Computer models have it tracking W/NW over the next several days, being steered by the subtropical ridge in the Northern Atlantic Ocean.

Currently, wind shear around Invest 90L is low, but the system may encounter some shear as it moves across the Atlantic, nearing the Lesser Antilles.  While encountering the higher shear, it should be slower to develop.

We are also watching another area of disturbed weather around the Lesser Antilles, moving into the Caribbean.  Expectations for development are low for development, as this system will be encountering higher wind shear.

Strong Saharan Air Layer (SAL)

Posted by Andy Johnson under Daily updates

Many of the disturbances that eventually develop into hurricanes originate in Sahel region of Africa. The Sahel region extends from the country of Senegal eastward to the Red Sea. The Sahel is north of the equator but south of the large Saharan desert. In the summertime, the Intertropical Convergence Zone (ITCZ) moves north of the equator into the Sahel area causing widespread convection. Some of these convective cluster continue westward into the Atlantic and are the incipient disturbances for tropical cyclones. The Sahel is at the same latitude as the Cape Verde Islands. In order for tropical cyclones to develop, moist surface air is necessary. The air that moves westward from the Sahara in the summertime is very dry, warm and often has a lot of dust from the desert. The dry, dusty air stabilizes the air over the Atlantic and inhibits tropical cyclone development.  The McIDAS image below shows the current extent of the SAL from the African coast almost to the Lesser Antilles.

The enhanced satellite image below shows several tropical waves on the periphery of the SAL, which are being influenced by the SAL.

The water vapor satellite image below confirms that much of the eastern Atlantic that is affected by the SAL is also very dry. The driest areas are shown in red.

The current streamline and wind shear product below shows that much of the eastern Atlantic is in a weak shear area which is conducive for tropical development but, at the same time, the strong SAL is inhibiting development in the eastern Atlantic.

 The 72 hour streamline and wind shear forecast shown below indicates that wind shear will remain light in the eastern Atlantic and will be moderate in the central and eastern Caribbean.

Tropics unusually dry

Posted by Andy Johnson under Daily updates

Three tropical waves continue to move westward in the Atlantic basin. The westernmost wave is in western Gulf of Mexico and is being sheared by the TUTT low further west in Texas. Scattered convection has continued to move onshore over much of coastal Texas and Louisiana today but with no organization. Another upper level low is evident centered near Jamaica and is causing moderate shear in the central Caribbean. The combination of shear and a large amount of dry air on either side of the second wave near Trinidad and Tobago is inhibiting development. The third wave west of the Cape Verde Islands has the most concentrated convection but shows no signs of large scale organization. The wave is also moving into a large area of relatively dry air, especially for this time of year.

The water vapor channel satellite image below shows a large expanse of dry air (shown in red) extending from the Azores all the way to the Virgin Islands with another tendril extending into the eastern Atlantic ahead of the third tropical wave. Another large area of dry is located in the central Caribbean in associated with an upper circulation. More dry air extends from NE Florida into the Alantic.  

The image below shows a moderate area of shear in the Caribbean being caused by the upper low there. Shear is very low ahead of the third tropical wave in the eastern Atlantic but that wave is also moving into a much drier environment.

The image below is the 72-hour forecast value of shear overlaid on surface streamline wind flow. By then the wave just entering the Caribbean will have moved to the western Caribbean and Atlatic wave will be approaching the Lesser Antilles. Overall, the tropics are pretty quiet for this time of year. Remember, though, that 90% of tropical storms occur in August, September and October.

Dry slot in the tropics

Posted by Andy Johnson under Daily updates

There are 3 tropical waves we are following in the Atlantic basin. One is west of the Cape Verde Islands and is showing signs of some spin near the surface on its northern edge. Another tropical wave associated with a wind surge is northeast of Venezuela moving fairly rapidly westward. The first two waves are moving into a large slot of dry air that covers much of the tropical Atlantic. The third wave extends from the Central Gulf of Mexico southward into the western Atlantic. An upper level low west of the Gulf wave is causing shear over the wave. The combination of shear to the west and the landmass of Mexico and Central America should prevent this tropical wave from developing. The situation reminds me of Bonnie a few days ago, when there was an upper low to the west of Bonnie and dry was being entrained from the east.

The enhanced IR satelitte image below shows large convective clusters with the wave affecting Belize, Hoduras and the Yucatan Peninsula as it moves westward.

The water vapor image below shows an unusual amount of relatively dry air for this time of year in the Atlantic basin. The tropical wave approaching Trinidad and Tobago is basically surrounded by the dry air and the slightly more organized wave west of the Cape Verde Islands is moving into a drier environment, as well. The large area of dry air should inhibit tropical development over a large portion of the basin for the next few days, at least.

The streamline analysis shown below shows a slight circulation associated with the eastern Atlantic tropical wave. However, the wave is moving into an unfavorable area for  development due to drier air even though wind shear is light to the west of the system.  

The image below is the forecast streamline and shear analysis. The tropica wave east of the Lesser Antilles will move into an area of moderate shear over the next few days. Shear will remain light near the eastern Atlantic tropical wave. However, the streamline analysis below shows an open wave in a few days with no closed circulation.f

Bonnie gone, tropics quiet

Posted by Sheena Parveen under Daily updates

Remnants of what was Tropical Depression Bonnie are continuing to move inland over parts of Louisiana and Mississippi as a trough.  This system will continue to move inland, fizzling out.

There is one weak tropical wave off the Mexican coast, continuing to move West.  As this system moves on land, tropical cyclone formation will not take place.  Elsewhere, the Gulf and Caribbean are quiet with only unorganized areas of showers and thunderstorms.

A quiet set-up in the Atlantic is hindering tropical wave development; that, and the fact that there aren’t many waves moving off the West coast of Africa at the moment. . .

Water vapor imagery shows an upper level area of low pressure moving into the Gulf, with drier air indicated by red.  A more stable atmosphere will exist in the Gulf and Atlantic over the next few days as high pressure sets up.

Bonnie moving closer to Gulf of Mexico, weakening

Posted by Sheena Parveen under Daily updates

Bonnie, now a tropical depression as of 5pm Friday, is continuing to move West/Northwest around 18 mph and is slowly making way into the Gulf of Mexico.  Most thunderstorm activity is well to the North of the center as the storm is losing strength crossing over South Florida.  As of now, Tropical Depression Bonnie is staying poorly organized, but is sending moisture into the Tampa Bay area and Central Florida.

An area of high pressure over the Southeast as well as an upper-level low in the Gulf will continue to steer Bonnie to the West, then Northwest over the next 24-48 hours.  Dry air is located to the West of Bonnie, as well as higher wind shear.

The higher wind shear will cause unfavorable upper level conditions for Tropical Depression Bonnie as it moves into the Gulf of Mexico.  This will allow the storm to stay borderline tropical depression/tropical storm strength for a majority of its track across the Gulf until reaching land around Louisiana and Mississippi.

Bonnie will stay well to our South and Southwest as it moves across the Gulf Saturday morning, continuing to send us a breeze with periods of rain, mainly early Saturday.  Conditions may be favorable enough to allow Bonnie to strengthen back to a tropical storm Saturday afternoon, maintaining that strength as it reaches land, but no further strengthening will be expected.

Computer models are still in agreement with this path.

Satellite and radar imagery shows most of the moisture associated with Bonnie well to the North of the center, with minimal thunderstorm activity at this point. 

Bonnie headed toward South Florida.

Posted by Dave Osterberg under Daily updates

As of 5AM Friday, Tropical Storm Bonnie was still a minimal tropical storm. You can also se by satellite, that it is a small storm overall, and given the size and strength, it should have minimal impact in South Florida.  The only thing that has changed a bit in the past few hours, is it’s forward movement is a little faster. Thats good because it give Bonnie less chance of strengthening before moving over South Florida. With this fast movement, 1-3 inches of rain can be expected in South Florida with lesser amounts to the north. This would obviously not cause widespread flooding, and at this point even the Keys aren’t evacuating. Once Bonnie moves into the Gulf, it should continue WNW until a landfall along the Northern Gulf Coast, perhaps near New Orleans. That would bring the storm right over the area with the oil spill. It will be interesting to see what that does to the spill site. On one hand, it may break up some of that solid shield of oil, but on the otherhand, it may push more oil onshore.  Once Bonnie gets into the Gulf, given it’s forward movement speed and the fact that the upper low is still impacting it,  rapid intensification is not expected.  Thats great news, since we have seen what can happen when storms get into the Gulf. It may get a little stronger, but should maintain Tropical Storm status. Keep checking back to make sure Bonnie doesn’t decide to do something different this weekend.