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Remnants Of Gonzalo

200 AM AST Sat Aug 14 2021
35 MPH
1010 MB

Depression expected to become a tropical storm later today.


1. Tropical storm conditions are expected in portions of the Leeward Islands late Saturday or early Sunday, and are possible over the Virgin Islands and Puerto Rico on Sunday. The risk of strong winds will then spread westward to the Dominican Republic Sunday night and Monday.

2. Heavy rainfall could lead to flash and urban flooding over the Leeward and Virgin Islands. Across Puerto Rico, heavy rainfall may lead to flash, urban and small stream flooding, along with the potential for mudslides.

3. There is a risk of wind and rainfall impacts across Haiti, the Turks and Caicos Islands, the southeastern Bahamas, and Cuba next week, and interests in those areas should monitor the progress of this system.




A Tropical Storm Warning is in effect for...
- Antigua and Barbuda, Anguilla, St. Kitts and Nevis, and Montserrat
- Saba and Sint Eustatius
- Sint Maarten
- St. Martin and St. Barthelemy

A Tropical Storm Watch is in effect for...
- British Virgin Islands
- U.S. Virgin Islands
- Puerto Rico, including Vieques and Culebra

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.

Interests elsewhere in the Leeward Islands, as well as the Dominican Republic, should monitor the progress of this system. Additional watches and warnings will likely be required for these areas tonight or on Saturday.

For storm information specific to your area in the United States, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. For storm information specific to your area outside of the United States, please monitor products issued by your national meteorological service.

Key messages for Tropical Depression Seven can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT2 and WMO header WTNT42 KNHC and on the web at www.hurricanes.gov/graphics_at2.shtml?key_messages.

WIND: Tropical storm conditions are expected within the warning area over the Leeward Islands by tonight or early Sunday. Tropical storm conditions are possible over the Virgin Islands and Puerto Rico beginning on Sunday.

RAINFALL: The system is expected to produce the following rainfall amounts today into Monday:

Over the northern Leeward Islands and Virgin Islands...3 to 6 inches. This rainfall may produce scattered areas of flash and urban flooding.

Over Puerto Rico...3 to 6 inches. Heavy rainfall could lead to flash, urban, and small stream flooding as well as potential mudslides.

At 200 AM AST (0600 UTC), the center of Tropical Depression Seven was located near latitude 15.6 North, longitude 54.7 West. The depression is moving toward the west near 21 mph (33 km/h). A motion towards the west or westnorthwest with a gradual decrease in forward speed is expected during the next few days. On the forecast track, the center of the depression is forecast to move over the Leeward Islands tonight, over the Virgin Islands and Puerto Rico on Sunday, and then over the Dominican Republic on Monday.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts. Some strengthening is forecast during the next couple of days, and the depression is expected to become a tropical storm later today.

The estimated minimum central pressure is 1010 mb (29.83 inches).

While Tropical Depression Seven has maintained a irregularly shaped cirrus canopy of deep cold cloud tops near its estimated center, the convection does not appear well organized. Several SSMIS microwave passes between 2011 UTC and 2205 UTC did not reveal much organization under the cirrus, with just a few patches of deeper convection contributing to the larger stratiform region. A helpful ASCAT-B pass at 0030 UTC showed that the center was near the southeastern end of this cirrus canopy, and found peak winds lower than earlier today at only 27 kt. The 0000 UTC subjective Dvorak estimates were T2.5/35 kt from SAB and T2.5/30 kt from TAFB and the most recent objective ADT estimate was in between at T2.2/32 kt. A blend of these data support keeping the initial intensity at 30-kt for this advisory.

The small cyclone continues to move quickly off to the west at 280/18 kt. A large low- to mid-level ridge draped across the central and western North Atlantic is expected to maintain the system on a general west-northwest heading, though with gradual deceleration as the ridge is eroded some by a mid- to upper-tropospheric trough. The latest track guidance remains tightly clustered but a bit more poleward through the first 72 hours. Afterwards, more track guidance spread becomes apparent. A quick look at the latest ECMWF ensemble guidance suggest that some of this spread is driven by the forecast intensity of the system, with stronger members taking the cyclone on a more poleward track. For now, the latest NHC track forecast is fairly close to, but a little poleward of the previous track. This track remains close to the HCCA and TVCN consensus aids, and roughly splits the difference between the deterministic GFS and ECMWF model solutions.

The intensity forecast is somewhat conflicting. Even though both the GFS & ECMWF based SHIPS guidance depict low 200-850 hPa vertical wind shear between 5-10 knots over the next 48 hours, the depression is also embedded in very dry mid-level air, with 700-500 hPa layer mean relative humidity as low as 44 percent currently in the ECMWF-SHIPS. In addition, the system is moving rapidly westward, and a continued fast motion in the short-term may result in higher westerly mid-level shear which may have a larger than normal effect to a small tropical cyclone in a very dry environment. After 48 hours, vertical wind shear out of the northwest is expected to increase, ahead of a large upper-level trough digging southwestward, upstream of the cyclone. Moreover, land interaction with both Puerto Rico and Hispaniola remains a distinct possibility, especially if the cyclone tracks left of the current forecast track. It is worth noting the latest HWRF run continues to be a extreme outlier with a much higher intensity than the remaining guidance. In fact, much of global model guidance and COAMPS-TC regional hurricane model barely maintains a closed circulation over the next 36-48 hours. I have elected to maintain a very similar forecast to the previous advisory, with peak winds of only 45 kt in 48-60 hours. This forecast remains conservative and is still lower than the SHIPS and HCCA intensity guidance.

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Sources include nearest National Weather Service office, National Hurricane Center, and the Florida Public Radio Emergency Network (@FloridaStorms).
Sources include nearby emergency management agencies, FEMA, and your local NPR affiliate. 
Sources include the Florida Department of Transportation, Florida Highway Patrol and other nearby traffic information.

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