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Tropics beginning to heat up

By: Dr. Jeff Masters, 5:20 PM GMT on August 21, 2005

The tropics are beginning to heat up again, and the current period of calm will likely be short-lived. There are three areas of possible tropical development worth mentioning today, and we will also discuss the possibility of extremely active conditions developing 7-10 days from now.

Yucatan and southern Gulf of Mexico
A strong tropical wave crossing Mexico's Yucatan Peninsula has an impressive and increasing amount of deep convection, and already appears to be gaining some rotation. Once the center of this circulation moves out over the warm waters of the Gulf of Mexico on Monday, chances are good that a tropical depression will form. An Air Force hurricane hunter aircraft will investigate tomorrow afternoon, if neccessary. If a depression does form, it will move west-northwest and probably make landfall in Mexico, under the steering flow of a strong upper-level high located over the southern Gulf states. This quasi-stationary high has been in place for a number of days, and is not forecast to move much the next few days. This high will act to protect the Gulf Coast of the U.S. both by steering potential tropical storms westward towards Mexico, and by using its strong shearing winds to tear apart any systems that venture too close to the Gulf Coast.

Cape Verdes Islands tropical wave
The vigorous tropical wave that pushed off the coast of Africa Friday night is now just southwest of the Cape Verdes Islands. The wave has a large circulation centered at 13N, and some strong deep convection to the south over the ITCZ with surface winds of 15-20 knots. Waters are warm, shear is light, and some computer models predict this wave will develop into a tropical storm. The GFS model predicts that a tropical storm will form from this wave on Wednesday and recurve in the center of the Atlantic Ocean towards the Azores Islands by early next week.

Remains of TD 10
The remains of TD 10 are just north of Hispanolia, and kicking up some moderate convection there. No circulation is apparent on satellite imagery, and surface pressures are not falling in the region. Although shear values are currently low, the remains of the depression are tracking due west towards Cuba and towards the shearing winds of the strong upper-level high over the southern Gulf states. This system will bring strong winds and heacy rain to the Bahamas and Cuba, but for now appears unlikely to develop into a tropical storm.

Forecast for 7-10 days from now
The GFS has been consistently predicting a very active period of hurricane development beginning late this week and running through the the end of the 16-day forecast period of the model. In my previous blog entry from Friday, I posted the GFS forecast for August 31, showing its prediction of three simultaneous tropical cyclones in the Atlantic. One and a half days later, the GFS is still predicting three tropical cyclones for August 31--although the northernmost one wasn't predicted last Friday, and is in fact the storm that is predicted to form from the current tropical wave just southwest of the Cape Verde Islands.

It bears repeating that computer forecasts of specific tropical storms developing are VERY unreliable--particularly out seven days and more from now. The GFS is likely to be dead wrong about the specific timing of the tropical waves moving off the coast of Africa, which waves might develop into hurricanes, and where in the ocean they may develop. What is believable is the GFS's forecast of a fundamental shift in the general atmospheric circulation leading to an enhanced period of hurricane activity starting later this week.

Jeff Masters

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