Tropical Development In W. Caribbean late in week

Posted By: Marty

Tropical Development In W. Caribbean late in week - 10/10/11 12:42 PM

I am still looking at the possibility of tropical development in the western Caribbean as early as this coming weekend with both the European and European ensemble guidance being consistent on this development. As I mentioned yesterday, the feature that will initiate this tropical cyclone development appears to be a tropical wave which is about to track across the Lesser Antilles. This tropical wave will move into the central Caribbean by about Wednesday morning and the western Caribbean by about Friday and Saturday.

The European model forecasts the development of a tropical cyclone just southwest of the Cayman Islands on Saturday and forecasts this potential storm to track west-northwestward across the Yucatan Peninsula next Monday and Tuesday and then start turning more northeastward just north of the Yucatan Peninsula next Wednesday.

The European ensemble guidance also forecasts the development of a tropical cyclone in the western Caribbean on Saturday and forecasts this potential storm to slowly track northwestward across the northwest Caribbean right through next Wednesday when it will be approaching the Yucatan Channel.

Crown Weather on October 10, 2011, 6:59 am
Posted By: Marty

Re: Tropical Development In W. Caribbean late in week - 10/21/11 12:54 PM

Potential Tropical Troubles In The Caribbean Over The Next Week

We are watching an area in the North Atlantic Basin, a broad area of low pressure centered just east of Nicaragua.

This system in the Caribbean continues to show some signs of organization. Surface data shows a broad counter-clockwise wind flow from just south of Jamaica to just east of Nicaragua. We have also observed persistent thunderstorms along and just east of the Nicaraguan coastline. If surface pressures in this area start to fall, this system could slowly form into an organized tropical system, perhaps as early as this weekend.

Computer forecasts suggest this system will track into the western Caribbean early next week and either move into Belize or remain nearly stationary.


There is an area of low pressure that is located over the southwestern Caribbean. Satellite imagery showed some concentrated areas of convection just east of the coast of Nicaragua. Vorticity in the area remains quite concentrated, centered near 12 North Latitude, 80 West Longitude. Wind shear has decreased since yesterday, as expected, and is currently between 10 and 20 knots. An area of 5 knots or less shear is expected to move over this system within the next 24 hours and environmental conditions are forecast to be favorable right through this weekend.

I expect slow development of this broad area of low pressure this weekend and I still expect it to become a tropical depression either on Sunday or Monday. Where will this potential tropical cyclone track? Currently this system is in an area of very light steering winds and it seems like it will very slowly track south-southwestward over the next day or two.

There are two potential scenarios for this tropical system. The first is that it meanders around the southwestern Caribbean over the next few days and gains little latitude. Should this happen, then a ridge of high pressure building over the southeastern United States and Gulf of Mexico early next week would likely push this potential tropical storm westward into Honduras and Nicaragua by about Tuesday and Wednesday. If this happens, then I foresee this to peak out as a 50 or 60 mph tropical storm, at most. This is the scenario laid out by the GFS model and the experimental FIM model.

The second potential scenario is that the trough of low pressure currently located over the eastern United States may be strong enough to lift this northward over the weekend as forecast by the Canadian, UKMET and NAM models. Should this happen, then it would have a lot more time to strengthen and could impact the Cayman Islands, central and western Cuba and the Yucatan Peninsula as at least a Category 1 hurricane right around the middle part of next week.

I am leaning towards the second scenario of this system lifting northward and potentially affecting the northwestern Caribbean and potentially south Florida and the Bahamas. With that said, western Caribbean tropical cyclones are notoriously very difficult to forecast and many things may change in the forecast of this potential tropical system over the weekend and into next week; so, stay tuned!

Crown Weather
Posted By: Marty

Re: Tropical Development In W. Caribbean late in week - 10/21/11 06:52 PM

Jeff Masters

A region of disturbed weather in the Western Caribbean (Invest 96L) is bringing heavy rains to coastal Nicaragua, and has the potential to develop into a tropical depression this weekend. Visible satellite loops show that 96L is beginning to show signs of organization. Some rotation is apparent, and the upper-level cirrus clouds streaming away from the center indicate that 96L is establishing an upper-level outflow channel to the east. The heavy thunderstorm activity is quite limited at present, because a large region of dry air to the east of 96L is interfering with development, as seen on water vapor satellite loops. An ASCAT pass at 11:05 am EDT showed no signs of a surface circulation, with surface winds in the 25 - 30 mph range. Surface pressures are slowly falling at San Andres Island, near the center of 96L. Wind shear is a moderate 10 - 20 knots in the region, and is expected remain in the moderate range through Monday. Water temperatures are very warm, 29 - 30C, and these warm waters extend to great depth.

Figure 1. Afternoon satellite image of 96L.

Forecast for 96L
The moderate wind shear and warm waters should allow some modest development of 96L over the next few days, though this will be slowed by the dry air to the storm's east. The models are quite enthusiastic about developing 96L into a tropical depression, and our top four reliable models for forecasting genesis--the ECMWF, GFS, UKMET, and NOGAPS--have all been predicting formation of a tropical depression by Monday in one or more of their runs over the past day. 96L is in an area of weak steering currents, and will move little over the next three days. On Tuesday and Wednesday, a strong trough of low pressure will be passing over the Eastern U.S., and this trough has the potential to turn 96L northwards into Cuba. This is more likely to happen if 96L is stronger and deeper, and thus able to "feel" the upper-level winds the trough will bring. The 12Z run of the GFS model and 00Z runs of the ECMWF and UKMET models predict 96L will develop into a tropical storm that hits Western Cuba on Wednesday or Thursday, and potentially affecting the Cayman Islands, South Florida, and the Bahamas as well. If 96L remains a weak and shallow system, it is more likely to stay trapped in the Western Caribbean and make landfall in Nicaragua. This is the solution of the NOGAPS model, which has 96L moving ashore on Tuesday over Nicaragua as a weak system. NHC gave 96L a 30% chance of developing into a tropical depression by Sunday in their 8 am Tropical Weather Outlook. A hurricane hunter mission is scheduled to investigate 96L Saturday afternoon.

I'll have a new post on Saturday, but might wait until the afternoon, when the hurricane hunter data becomes available.

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