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Invest 96L Progresses Towards the Leewards; An Unclear Threat Down The Road

By: Hurricane1216 , 3:41 AM GMT on August 22, 2014

Invest 96L continues to show signs of organization as it trudges towards the Leeward Islands this evening. According to the last entry into the ATCR (0000z), the disturbance did contain tropical storm-force winds of 35 kts and possessed a pressure of 1009 mb. The motion of the storm given the past two fixes of 96L yields a WNW (305 degree) motion at around 23 mph (38 km/h), which correlates with what recon was fixing earlier today. As of the latest Tropical Weather Outlook, the NHC has the odds of tropical cyclogenesis for 96L within 2 days at 60%, and the odds of cyclogenesis within 5 days at 80%. Due to the currently low confidence in the future track of 96L, the NHC's experimental 5-Day development polygon for 96L extends as far west as the Florida Keys and as far north as near Bermuda. Interests in these areas should keep a very close eye on 96L as it continues to track westward. Within the last few hours, convection appears to have built over the supposed circulation center of 96L, which is a sign of centralized strengthening and organization. Despite indications earlier today that the disturbance may have lost some of its previous luster, recon earlier this afternoon hinted at the prescense of gale-force (tropical-storm force) winds to the north of the dominant center of 96L, and the overall appearance of the system appears to have improved since then. Reconnaissance did find a potentially competing circulation center within 96L, and satellite imagery at dusk did hint at the possibility of developing vorticies, though at this point in time it would appear that a dominant center is taking shape northeast of Guadeloupe. Radar imagery out of Martinique (courtesy of Meteo-France) seems to indicate such a center tracking a general westward motion into the Leeward Islands.

Figure 1: 0109 UTC (about an hour or so old from the posting of this post) AMSU 89 GHz microwave imagery of 96L showing convection building internally within the storm.

A Rainmaker For The Leewards
Although the main questions in the weather communities tonight have been things like "How strong will 96L get?" and "Will it hit the United States?", right now Invest 96L is honing in on the Leeward Islands and Puerto Rico. Radar out of Martinique indicates generally scattered shower activity from the incoming disturbance, with some tight cells with reflectivity values at around 50 dBz. These rains in short bursts can cause gusty winds and localized flooding. A FLASH FLOOD WATCH IS IN EFFECT FOR MOST OF PUERTO RICO AND THE VIRGIN ISLANDS, and this is a result of the potentially hazardous bursts of rainfall that can be produced in short periods of time by these tropical systems. Radar out of San Juan shows these scattered cells moving northeast to southwest across the area with about 1"/hr rainfall rates. However, overall storm total radar estimates have indicated that as much as 3" of rain has fallen in northern Puerto Rico. Though at times hazardous, these rains should help to alleviate some of the drought in Puerto Rico, which according to the National Drought Mitigation Center has worsened since the passage of Tropical Storm Bertha earlier this August. Reports from volunteer hurricane correspondents on the stormCARIB network are confirming the intermittent occurrence of these showers. Barring any significant change, this pattern should continue as Invest 96L tracks through or north of the islands. In regards to winds, the possibility exists for the Virgin Islands and Puerto Rico to receive tropical storm force winds. However, this is largely dependent on the positioning of 96L as these winds are confined to the northeastern quadrant of the system. A more southerly track would put these winds over the islands, but a more northerly track may help to mitigate these winds. Nonetheless, the bands surrounding the center of 96L may produce damaging wind gusts.

An Unclear Future
To say the least, the track forecast for 96L remains fuzzy. Despite appearances that the steering for 96L will be seemingly straightforward and appearances that there is a consensus between models, the potential model solutions are out there, and there is a wide range of possibilities for where 96L may end up. Ensembles are showing pretty huge spreads for the track forecast in regards to the disturbance. The positioning of 96L in the future is greatly dependent on the forward motion of the disturbance, its intensity, and the timing of the trough north of the Greater Antilles and the timing of the ridge that is perhaps expected to build over the northeastern United States / eastern Canada. Right now, the only track we're pretty sure of is a track over or a touch north of the Virgin Islands / Puerto Rico, and after that things get blurry. If 96L is able to make it into the area north of Puerto Rico / Hispaniola quick enough, it should be able to catch the trough over the region and race off out to sea, which is a solution that many of the models like the GFS are looking at right now. However, a slower system in that area may lead to two things. A) The system lingers around the Bahamas for a bit and then moves off into a direction unclear at this point in time, but likely NE, and B) The system is able to sneak under the building ridge to the north and make a run towards Florida. Though the variables in that area are currently too unclear to make a very confident forecast, I am thinking that 96L will be able to make it to around Bahama's Crooked Island before heading northward. However, another forecasting variable exists in the general path of 96L - Hispaniola. Known for being able to sap the lives of tropical cyclones in times past, the motion of 96L from most likely a bit ENE of the island changes the island's role from a complete circulation shredder to more of a potential director in regards to 96L's motion. The northern coast of Hispaniola may help to tighten any potential circulation and perhaps steer a future-04L further westward, threatening Florida. The HWRF paints a very wary forecast for the storm, projecting a near or major hurricane near the Miami shores after interaction with Hispaniola. Although we're hoping for this potentially catastrophic solution not to occur, we cannot discard the HWRF forecast since atmospheric patterns can lead to its verification with just a few changes. That said, I think the chances for a storm moving into the Gulf of Mexico from the Florida Straits or the Caribbean Sea are lessening but still not completely out of the picture.

Figure 2: Some model tracks (21/0000 UTC) for 96L.

As 96L is still NOT a tropical cyclone and is still east of the Lesser Antilles, those monitoring this system should closely watch for general trends in models and look at the overall picture instead of putting too much weight into every single individual model run at this point in time. Models have a tendency to be bipolar when systems are not very well defined and are still developing. When this system develops, if it does, more weight can be given to the individual models, and of course to the NHC's official forecast. That said, mind the weather, and keep a close eye on the tropics at all times.


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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3. WunderAlertBot (Admin)
9:41 PM GMT on March 20, 2015
Hurricane1216 has created a new entry.
2. Hurricane1216
2:39 PM GMT on August 23, 2014
Quoting 1. Cscrep19:


BBC News has got this track on this website ; http://www.bbc.co.uk/weather/4164138 <---It shows down on the radar that it will track south-west and then track to Gulf of Mexico.

Not as of this point -- whatever model the BBC uses now has it approaching the coasts of Georgia and South Carolina.
Member Since: December 31, 1969 Posts: Comments:
1. Cscrep19
5:45 PM GMT on August 22, 2014

BBC News has got this track on this website ; http://www.bbc.co.uk/weather/4164138 <---It shows down on the radar that it will track south-west and then track to Gulf of Mexico.
Member Since: December 31, 1969 Posts: Comments:

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High school student, loves the weather, but could do without the Texas heat. Lurker/poster on WU since 2006. Hook 'em Horns!

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