98L forms and Saharan Air pushes across the Atlantic

The north Atlantic is once again active with an intermittent low pressure system, the models are forecasting a slow uptick in the Mean Development Region (MDR), and Florida will become a bit dusty. This comes during the time of year that generally sees the tropics come alive and Florida is mid-rainy season.

Over the last day or so an area of low pressure has developed northeast of the island of Bermuda. Earlier today, the NHC went ahead and designated the area of low pressure as an invest with the alphanumeric 98L. 98L has winds of 35 mph according to my estimate based on scatterometers and recent satellite trends and a minimum central pressure of 1008 millibars. Earlier today, a case could have been made for an upgrade to Tropical Storm Ernesto, however thunderstorms have since waned. Throughout today I could really never conclusively say that this is a tropical system and the NHC agrees that this is a non-tropical system. If thunderstorms return during the next 12-18 hours, I think there is a fairly decent chance of a tropical conversion and an upgrade to tropical storm status, and according the NHC the chance is 40%. I think atmospheric conditions should be favorable for the next few days, however the limiting factor will be cool sea surface temperatures. Amply warm water will begin to run in short supply in about 24 hours. There is a fairly strong low level circulation with an evident dry center, and thus convection shouldn’t be to horribly hard to come by. I am forecasting a regeneration of convection by noon tomorrow that will be intermittent in nature. I’m not yet sure if this will be enough to designate it a tropical storm. Watch my twitter tomorrow for updates on this.

The following image shows the canopy structure of 98L as well as the underlying thunderstorms. Not that these images were taken three hours apart. In the left image, the bright reds indicate stronger thunderstorms. In the right image, the bright yellows and oranges indicate higher cloud tops.

In terms of the MDR right now, the NHC seems to be in a wait and see mode as they should be. A rather robust tropical wave is moving westward off the coast of Africa. According to ASCAT, it has a good circulation to the southeast of the Cape Verde islands somewhat removed from the deepest thunderstorm activity. The models that are flirting with development show slow to nonexistant development until about 55 to 60W in longitude, which would place the wave northeast of the Lesser Antilles. There is a very high likelihood that the dry air of the eastern Atlantic will eat away at this system before it even makes it to 50W, but I will watch the system.

Bringing it back home, Florida will be experiencing an abnormally dry end of the week this due to the Saharan Air Layer, which is the same airmass that will plague the tropical wave mentioned above. SAL can be seen in the blues and greens in the image below protruding into the western Caribbean and the Florida Keys. This air will make it as far north as I-4 by Friday, which will drop rain chances to less than 20% and raise afternoon temperatures into the mid to upper 90s for the southern half of the state starting Thursday and beginning to end on Sunday. A southwesterly regime will set up with high pressure drifting to the south by Friday, which means morning showers at the beaches on the west coast and afternoon storms on the east coast. This dry air doesn’t necessarily lower the intensity of storms but it will certainly lower the number of storms that develop each day.

Another side effect of this Saharan air is that it will create beautiful sunrises and sunsets due to the additional amount of particles sunlight must pass through to reach your eyeballs. If you get a good shot of the sun on the horizon or a general thunderstorm…tweet me at @JonathanBelles with your pictures and i’ll share them with everyone! I’ll see you all soon!


Posted on Tuesday, July 24th, 2012, in Florida Weather, Tropical Weather. Bookmark the permalink. Leave a comment.

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