Alberto Gone, Watching the Caribbean


At 11am EDT today, the NHC issued the last advisory on Tropical Depression Alberto. Wind shear has taken its toll on the system leaving Alberto looking like this sloppy mess at the time of the last advisory:

Alberto RGB Image

Regeneration is not expected from Alberto.

Western Caribbean Disturbance:

There has been a persistant area of low pressure over the Western Caribbean the last week. Throughout this time, a lot of cyclonic turning in the lower levels of the atmosphere has been observed, but wind shear has just been too strong to allow anything to develop. Satellite imagery over this area shows an increase in convection today:

Visible Satellite Image of the W Carib

The predominant area of vorticity had previously been just off the coast of Belize. However, today a new area of convergence and vorticity has been centered just west of the Cayman Islands.

As already said, the main inhibiting factor to development has been the subtropical jetstream, which is providing wind shear in excess of 20-30 knots. Over the past 24 hours shear is starting to decrease, although it is still about 30 knots over the main area of vorticity and convection:

15Z Wind Shear Analysis

Wind shear quickly increases to the North of the disturbance. The GFS has been suggesting that if the disturbance can stick around long enough (roughly by Wednesday Night) in the Western Caribbean without getting pulled out to the NE, then wind shear will lessen to levels that are conducive for development. Here is today’s 12Z 200mb forecast for 00Z Thursday (8pm Wednesday Night EDT):

12Z GFS 36 hour 200mb forecast

Notice the subtropical jetstream still resides over the Gulf of Mexico and NW Atlantic, but upper-level winds over the NW Caribbean are <10 knots and that is very favorable to cyclogenesis. It is possible that if positioned correctly, the subtropical jetstream could act as an outflow channel to this disturbance, which would also aid development. Given that there is already a good deal of lower level vorticity in the region, it may not take much to get a cyclone to develop in this area. It seems the main variable is time. Will the disturbance remain in the Caribbean long enough to take advantage of these more favorable conditions?

At the moment all of the reliable computer models are not forecasting tropical cyclone development in the Western Caribbean. Instead some are suggesting that development may take place in 3-5 days, north of the Bahamas, as the disturbance moves north of the subtropical jetstream. I am very skeptical of this given the GFS upper-level forecast. In my opinion, the best shot we will see for development is tomorrow night if the disturbance is still in the Caribbean. If this occurs, I would give the area of interest a 40% chance of becoming a tropical cyclone.

Regardless, it would not surprise me to see this area get tagged as Invest 94L either today or tomorrow as well as seeing the area be mentioned in a special Tropical Weather Outlook by the NHC. Even if the system does not develop into a tropical cyclone, the disturbance will dump very heavy rainfall over the Cayman Islands, Jamaica, Cuba, and the Bahamas and the potential for flooding exists. Interests in these areas should stay alert for this threat.

I’ll have an update again on this feature when conditions warrant as well as an update on Tropical Storm Bud later today.



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