Shower and thunderstorms associated with an elongated area of low pressure several hundred miles east of the Windward Islands has become a little better organized. Additional slow development is possible and this system could become a tropical depression during the next day or two as it moves west-northwest at about 10 to 15mph.
Tropical Atlantic Wide Infrared Satellite Image:
USA National Weather Service Forecast
6:00 am EST on August 21, 2014
For the North Atlantic...Caribbean Sea and the Gulf of Mexico:
Showers and thunderstorms associated with an elongated area
of low pressure located a few hundred miles east of the Windward
Islands have changed little in organization during the past
several hours. Environmental conditions are expected to be
conducive for development during the next couple of days, and a
tropical depression could form while the system moves
west-northwestward at 10 to 15 mph across the Lesser Antilles and
over the eastern Caribbean Sea. The mountainous terrain of
Hispaniola and eastern Cuba could limit development during the first
part of the weekend, but conditions are expected to be conducive for
development early next week when the system is forecast to move near
or over the Bahamas.
Regardless of tropical cyclone formation, gusty winds and heavy
rainfall are possible across portions of the Lesser Antilles, Puerto
Rico, and the Virgin Islands tonight and Friday, and over Hispaniola
late Friday and Saturday. Interests in those islands should closely
monitor the progress of this disturbance. An Air Force Reserve
hurricane hunter aircraft is scheduled to investigate the low this
afternoon, if necessary.
* Formation chance through 48 hours...medium...50 percent.
* Formation chance through 5 days...high...70 percent.
48 Hour Forecast – Favorable Environmental Conditions For Tropical Development
Infrared Satellite in Belize City
Tropical Development May Be Imminent in Atlantic
8/21/2014 3:50:23 AM
We are continuing to monitor the progress of a tropical wave near 55 West and just south of 15 North that show signs of organized convection which could lead to the broad, elongated area of low pressure to deepen and quickly spin up in to a tropical depression during the next 48 hours. If this were to happen this tropical wave could eventually become a tropical storm by early next week, and would be named Cristobal. The most immediate impacts of this feature will be felt across the Lesser Antilles, Virgin Islands and Puerto Rico with gusty winds and heavy showers, beginning tonight and continuing through Friday.
The uncertainty of how quickly this feature develops is due to current upper-level easterly shear. This could limit development the next 24-48 hours, but computer models show the shear lessening in the path, so it could strengthen as long as it does not interact with too much land over the northern Caribbean. Most model output suggests that an upper-level trough and developing low pressure area east of the mid-Atlantic coast draws the system farther north across the Bahamas late this weekend and that the system does not go into the Gulf of Mexico. This is not yet set in stone, but it appears more likely than a scenario into the Gulf of Mexico. All interests in the Caribbean and along the Gulf and southeastern U.S. coasts should monitor this system.
Elsewhere, an area of low pressure near the mid-Atlantic coast is projected to move east and could strengthen some. The system will move over marginally warm water but will be impacted by strong upper-level westerly shear. Still, it's not out of the question that it could become a hybrid or subtropical low pressure system over the next several days. Also, a tropical wave is out near the Cape Verde Islands will trek westward the next few days days, but computer guidance does not show any really development of this wave until early next week.
120 Hour Forecast – Favorable Environmental Conditions For Tropical Development
Invest 96L Still Slowly Organizing & Will Impact The Central & Northern Lesser Antilles, Virgin Islands & Puerto Rico With Heavy Rain Squalls & Gusty Winds From Tonight Into Friday; Lots Of Uncertainty In Longer Range With The Potential Track Of Invest 96L
Rob Lightbown of Crown Weather Services
Thursday, August 21, 2014 8:18 am
Invest 96L, which is located about 350 miles to the east of the Lesser Antilles or near 58 West Longitude this morning, continues to slowly become better organized with some thunderstorms popping up around the broad area of low pressure. In addition, it looks like this system’s overall structure is gradually improving as well. A look at the environmental conditions around Invest 96L shows that conditions are becoming more favorable for it to continue to organize and strengthen. We clearly see that there is an area of high pressure nearly on top of 96L which is imparting little or no wind shear. In addition, an upper level low pressure system just east of the Bahamas is helping to ventilate Invest 96L leading to this gradual increase in organization.
These improving environmental conditions will continue through at least Friday as Invest 96L tracks across the central and northern Lesser Antilles tonight and across the Virgin Islands and Puerto Rico during Friday. Given the improving environmental conditions, along with Invest 96L gradually becoming better organized, I do think that there is a relatively high chance that we will see this system upgraded to a tropical depression as early as late this afternoon or this evening.
Even if Invest 96L is not upgraded to a tropical depression later today, it will still bring gusty winds with wind gusts of up to 40 mph, heavy rain squalls and rough seas to the central and northern Lesser Antilles from today through tonight and to the Virgin Islands and Puerto Rico from tonight into Friday. Please be aware of this if you live in or are vacationing in the central and northern Lesser Antilles, Virgin Islands or Puerto Rico.
This system is then forecast to track very near, if not right over Hispaniola on Saturday where this system will bring heavy rainfall and gusty winds to much of the Dominican Republic and Haiti throughout Saturday.
Most of the forecast guidance is showing that Invest 96L will track into the southern and central Bahamas from about Sunday to possibly Tuesday where environmental conditions will be favorable for strengthening. In fact, some of the global models are suggesting that the upper level environment may be very favorable leading to significant strengthening. Everyone in the central and southeastern Bahamas, as well as the Turks and Caicos Islands should closely monitor Invest 96L as I think there is a fairly good chance that it will impact you with at least tropical storm conditions throughout Sunday and Monday and possibly into Tuesday.
Beyond this, a large chunk of the global models, including the GFS, Canadian and European model guidance now are showing a further east track leading to this system curving off of the US East Coast and possibly threatening Bermuda. The reason for this is that currently we have a weakness in the high pressure system that currently extends from off of the US East Coast to the Gulf of Mexico. This weakness is currently located just to the east of the Bahamas. It seems that a majority of the models are forecasting that this system will be tugged northward towards this weakness and eventually pulled northeastward out into the open Atlantic by a trough of low pressure pushing off of the US East Coast later next week. Is this a possibility? Yes, most definitely.
Now, not all of the global models are forecasting this system to track out into the open Atlantic after it tracks through the Bahamas late this weekend and early next week. The UKMET model insists on a west-northwest to northwest track that threatens the Florida Keys and south Florida by Wednesday of next week. In addition, the HWRF model, which is a model designed to specifically forecast tropical storms and hurricanes, forecasts a track that takes this system across all of the Bahamas on Sunday and Monday as a strengthening tropical storm that eventually becomes a hurricane. The HWRF model ends with a forecast of this system coming ashore in southeast Florida on Tuesday of next week as a hurricane. Why are these two models forecasting such a different outcome? Looking at the UKMET model’s forecast upper air pattern, it shows that a skinny ridge of high pressure may build southwestward from New England into the Mid-Atlantic states and Carolinas by Monday which would block this system from tracking into the open Atlantic.
I want to strongly point out that you should not be focusing on any one model forecast. These various model forecasts have changed dramatically over just the last couple of days with some models showing upwards of a 1000 mile difference in the forecast track of Invest 96L in just 24 hours time. The track that this system takes depends heavily on the timing and position of any ridges of high pressure or troughs of low pressure which could either block it from tracking out into the open Atlantic or help it track out into the open Atlantic, the actual strength of the storm and the actual position of the storm.
It is important to note that we should be looking at the overall pattern that each of these models are showing rather than the specific details of where a storm may or may not be. So, even though the various models are showing a plethora of different solutions and possible tracks from one model run to another, there seems to be two potential scenarios. The first is for the tropical system to track across the central and southern Bahamas late this weekend and early next week and then be picked up by an upper level trough of low pressure and pushed north and northeastward fairly far offshore of the US East Coast. The second potential scenario would keep this tropical system on the south and southwest side of a high pressure ridge leading to a track across the Bahamas and a viable threat to the Florida Peninsula as outlined by the UKMET and HWRF models.
Right now, the models seem to be favoring the first scenario described above, but it is very possible for these models in the coming days to shift back to the second scenario described above, resulting in a more westerly track and a storm that threatens the Florida Peninsula and the eastern Gulf of Mexico. It goes without saying that the overall uncertainty of where this system will track after this weekend is just too large. Everyone across the central and eastern Gulf of Mexico, Florida Peninsula and US Southeast coast should keep close tabs on the progress and forecasts with Invest 96L over the next several days. There is nothing to worry about at this time, just keep a close watch on this system, that is all.
I will continue to have frequent updates on Invest 96L as conditions warrant.
Invest 96L Information:
Model Track Forecast:
Disorganized 96L Bringing Heavy Rains to Lesser Antilles
3:05 PM GMT on August 21, 2014
Heavy rain showers are sweeping through the Lesser Antilles Islands as a strong tropical wave (Invest 96L) heads west-northwestwards at about 15 - 20 mph through the islands. Satellite loops on Thursday morning showed a pretty unimpressive system, with a broad, elongated surface circulation and a modest amount of heavy thunderstorm activity that had changed little in intensity or organization since Wednesday. The storm was poorly organized, with a clumpy appearance and just a few small low-level spiral bands. Radar loops from Barbados and Martinique showed only a slight amount of rotation in the radar echoes. An 8:37 pm EDT Wednesday pass from the ASCAT satellite showed top surface winds near 35 mph on the east side of 96L. Wind shear is moderate, 10 - 20 knots, and water vapor satellite images and the Saharan Air Layer analysis show that 96L has moistened its environment considerably since Wednesday, though some dry pockets persist in the vicinity, particularly to the west. Sea Surface Temperatures (SSTs) are near 28°C, which favors development.
Forecast for 96L Given 96L's disorganized appearance on satellite imagery, the Thursday afternoon flight of the Hurricane Hunters may get cancelled. The earliest I would expect 96L to become a tropical depression would be Friday morning. The 0Z Thursday runs of our three most reliable models for predicting tropical cyclone genesis, the UKMET, GFS, and European models, had one model, the UKMET, predicting potential development into a tropical depression by Saturday. The storm will pass through the Lesser Antilles Islands Thursday and Friday, bringing heavy rain showers and strong winds, which will also affect the Virgin Islands, Puerto Rico, and Dominican Republic Friday through Saturday. A Flash Flood Watch is in effect from late Thursday night through Saturday morning for the Virgin Islands, Puerto Rico, Culebra, and Vieques. Rainfall amounts of 4 - 6" with locally higher amounts are expected.
Figure 2. Latest satellite image of 96L.
The circulation center of 96L has jumped considerably to the northwest over the past day, resulting in northward shifts in the expected track of the system from all of the major models. On Saturday, 96L may pass near or over the islands of Puerto Rico and Hispaniola, whose rugged terrain would likely disrupt the storm. By Sunday, 96L is expected to be near the Southeast Bahamas and Turks and Caicos Islands, and both the GFS and UKMET models predict that 96L will be able to develop into a tropical depression by Sunday or Monday. The 8 am EDT Thursday run of the SHIPS model predicted that wind shear would stay in the moderate range, 10 - 20 knots, though Sunday, then rise on Monday. With dry air expected to be in the region, wind shear would likely be able to drive the dry air into the circulation of 96L, keeping any development slow. A trough of low pressure is expected to be over the U.S. East Coast early next week, and the GFS and European models predict that this trough will be strong enough to turn 96L north and then northeast, keeping the storm away from the Southeast U.S. coast. However, long-range model forecasts of disturbances that haven't formed into a tropical depression yet are unreliable, and we should not be confident that 96L will miss the Mainland U.S. yet. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day development odds of 50% and 70%, respectively.
CLICK HERE for the website for Belize National Emergency Management Organization (NEMO)