ITCZ

Earl, Ex-Gaston, Invest 99L…

Tropical Storm Earl has been bearing down on Nova Scotia with winds of 70 MPH, and the center is now inland and within 24-36 hours will be a post-tropical/extratropical system.

Ex-Gaston has continued to look somewhat healthy although the convection is west of the center but it is trying to redevelop back to a tropical cyclone. With the exception of some dry air, the environment will be favorable for continuing development and the forecast for Gaston is to become at least a Tropical Storm if not a Hurricane within the next few days. There is a TUTT in the area of PR and will continue to head SW and that will help develop an anticyclone that will possible be over Gaston – thus Gaston will be able to gather more strength and vent out. The direction for Gaston is simple, it will continue it’s westward drive. I feel it will stay that way till after it has passed through the Lee/Windward islands but later on it may want to take a more WNW- to NW direction. The forecast after that is still unclear.

Using the Shear map you can see the TUTT.

Invest 99L is disorganized system as it is very elongated from SW to NE. There is the possibility that the “center” could be within the ITCZ. If this were the case the models are going to incorrect. At the moment the models are forecasting a NW movement and away from everyone. If the convection is near that “center” within the ITCZ – we have a new ballgame. Until there is a better grasp on something that does not even have a LLC – an “accurate” forecast cannot be made.

In the BOC – there an area of disturbed weather. This looks to be some energy from the system in the Pacific – TD11-E. The shear in that area is very light (5-10 knots) and is conducive for some limited development. Is may start to head NW or NNW. Within 36-48 hours, shear will increase and interaction with the land masses will hinder further development.

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Invest 91L

This morning an area of some very intense thunderstorms has become better organized and has now been designated as Invest 91L. The NHC has this system at a 60% chance of becoming a tropical depression by Tuesday morning. Satellite loop imagery is indicating that the intense thunderstorm activity and intensity has been increasing. The latest satellite images seem to indicate that 91L has very good cyclonic turning and may be beginning to form the surface circulation even though 91L is still within the ITCZ and still to close to the equator. This may be the beginning for 91L to break away from the ITCZ and if so then 91L may be classified as either a tropical depression or tropical storm later today or tonight.

With the SST’s in the area at around 29° centigrade and the SAL to the north of 91L along with the wind shear at 10-20 knots, further development is a distinct possibility. The only negatives for any development for 91L is the MJO, which favors downward motion over the tropical Atlantic and as stated earlier, being to close to the Equator.

Later in the week, as 91L approaches the Lesser Antilles, a strong upper-level low near Puerto Rico is forecast to bring high levels of wind shear. This would hamper any quick intensification. As usual, any long range forecasts will have changes so to state where and how strong any system will be is just speculation.

Steering layer forecasts to keep 91L on a WNW track at least for the next 1-2 days, after that a WNW – NW motion is forecast. All those in the Leeward Islands should keep a eye on 91L.

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Invest 90L

The tropical disturbance that had rolled off the coast of Africa yesterday has now been designated as Invest 90L. This system has very good cyclonic turning but the one thing that 90L has a problem with is that it is embedded within the ITCZ.  It will be very difficult to develop within the ITCZ as it has to compete with the surrounding convection along with the rest of the atmospheric conditions. Once it breaks free of the ITCZ and can maintain the convection on its own then there is good chance it will develop other wise it will just be stormy weather in South America. I do feel that 90L will break it self away from the ITCZ and models do think this may develop. The initialization of the models run are new and might have some bias in them.

Some may wonder why is the Invest number 90L instead of 100L. The invests start off with 90 and end at 99. Once 99L is used they return back to 90L.

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