Heavy Rainfall, Gusty Winds From Tropical Storm Grace Spreading Across Lesser Antilles

Tropical Storm Grace is moving across the Lesser Antilles, with scattered showers and thunderstorms affecting much of the island chain, though the strongest winds are still forecast to affect the Leewards.

Grace is forecast to move across the Leewards tonight into early tomorrow morning with tropical storm warnings in effect from Antigua and Barbuda to Puerto Rico, with tropical storm watches in effect for parts of the Dominican Republic.

Specifically for Trinidad and Tobago, while direct impacts are not expected, periphery impacts such as an atypical wind regime are expected from today (Saturday) through tomorrow (Sunday) with funnel cloud activity likely. There may also be the possibility of feeder bands (strong showers, thunderstorms, and gusty winds associated with Tropical Storm Grace) developing tonight into Sunday. An Adverse Weather Alert will in effect for T&T from 2:00 AM Sunday from the Trinidad and Tobago Meteorological Service at this time for T&T.

The Latest From The National Hurricane Center

Tropical Storm Grace's Forecast Track as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)
Tropical Storm Grace’s Forecast Track as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)

At 5:00 PM AST, the center of Tropical Storm Grace was located near latitude 15.9 North, longitude 60.7 West. Grace is moving quickly toward the west near 43 KM/H. A motion toward the west-northwest with a gradual decrease in forward speed is expected during the next several days. On the forecast track, the center of Grace is expected to move over the Leeward Islands tonight, near the Virgin Islands and Puerto Rico on Sunday, near or over the Dominican Republic Sunday night and Monday, and then near or over Haiti Monday night.

Maximum sustained winds are near 65 KM/H with higher gusts. Some strengthening is forecast during the next day or two. Grace is likely to weaken while it moves near and across the Greater Antilles Monday and Tuesday.

Tropical-storm-force winds extend outward up to 55 kilometers to the north of the center. The estimated minimum central pressure is 1010 millibars.

Tropical Storm Grace's Forecast Track as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)
Tropical Storm Grace’s Forecast Track as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)

Tropical Storm Grace’s Watches & Warnings

Tropical Storm Grace's Tropical Storm Watches and Warnings as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)
Tropical Storm Grace’s Tropical Storm Watches and Warnings as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)

A Tropical Storm Warning is in effect for:

  • Antigua and Barbuda
  • Anguilla
  • St. Kitts and Nevis
  • Montserrat
  • Saba
  • Sint Eustatius
  • Sint Maarten
  • St. Martin
  • St. Barthelemy
  • British Virgin Islands
  • U.S. Virgin Islands
  • Puerto Rico, including Vieques and Culebra

A Tropical Storm Watch is in effect for:

  • South coast of the Dominican Republic from Punta Caucedo to Cabo Engano
  • North coast of the Dominican Republic from Cabo Frances Viejo to Cabo Engano

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 Dominican Republic, Haiti, the Turks and Caicos Islands, the southeastern Bahamas, and Cuba should monitor the progress of Grace. Additional watches and warnings could be required for this area tonight or on Sunday.

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.

Tropical Storm Grace: Hazards Affecting Land

Tropical Storm Grace's probabilities for tropical-storm-force winds as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)
Tropical Storm Grace’s probabilities for tropical-storm-force winds as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)

WIND: Tropical storm conditions are expected within the warning area in the Leeward Islands tonight, and in the Virgin Islands and Puerto Rico on Sunday. Tropical storm conditions are possible within the watch area in the Dominican Republic Sunday night and Monday.

RAINFALL: Grace is expected to produce the following rainfall amounts Saturday into Tuesday:

  • 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 with isolated maximum totals of 8 inches. Heavy rainfall could lead to flash, urban and small stream flooding and possible mudslides.
  • Over Haiti and the Dominican Republic: 4 to 7 inches with isolated maximum totals of 10 inches. Heavy rainfall could lead to flash and urban flooding and possible mudslides from Monday into Tuesday.
  • By mid to late next week heavy rainfall from this system could impact portions of Cuba, the Bahamas and Florida.
Tropical Storm Grace's probabilities for hurricane-force winds as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)
Tropical Storm Grace’s probabilities for hurricane-force winds as of 5:00 PM Saturday 14th August 2021. (National Hurricane Center)

This system is of no direct threat to Trinidad and Tobago.

Tropical Storm Grace’s Forecast Discussion

Tropical Storm Grace (Weathernerds.org)

Grace is a poorly organized tropical storm this afternoon. The NOAA Hurricane Hunters were unable to close off a circulation, at least at their flight level of 5000 feet, but dropsonde observations and reports from some of the islands in the Lesser Antilles suggest that there’s at least a broad cyclonic circulation at the surface. The various data also indicate that the center has sped up, or re-formed, and is located farther southwest than previously estimated. Based on the aircraft data and earlier ASCAT data, the initial intensity is set at 35 kt.

Both the future track and intensity of Grace have a high level of uncertainty. For the track, the forecast is likely to be
complicated by the fact that the system doesn’t currently have a tight low-level circulation, and the center could always re-form at any time, especially with convection ongoing farther to the north. In addition, the storm has not yet slowed down, and in fact, the initial motion is estimated to be toward the west (275 degrees) at 23 kt. The guidance envelope has made a notable southward shift due to the adjustment of the initial position, and the models insist that Grace will primarily have a west-northwestward heading for much of the forecast period with the speed gradually decreasing during the next 48 hours or so. The NHC track forecast has been shifted southward accordingly, although any re-formations of the center could cause this track to shift again in future advisory cycles.

If Grace slows down as forecast–which is obviously not a sure thing–environmental conditions should be conducive to allow for some strengthening before the system reaches the Greater Antilles. The southward adjustment in the official forecast now takes Grace over the Greater Antilles for a longer period of time, and the official intensity forecast is, therefore, lowered beyond 48 hours. This is a middle-of-the-road solution, and actually lower than most of the intensity guidance. If the forecast track shifts north or south, the system could strengthen further over water. Alternatively, Grace could go the way of Fred and dissipate before the end of the 5-day period.

In the end, the exact track of the center and the intensity of the system will likely not be as important as the heavy rainfall that is forecast to fall across the Leeward Islands and the Greater Antilles during the next few days.

Key Messages:

  1. Tropical storm conditions are expected in portions of the Leeward Islands tonight, and the Virgin Islands and Puerto Rico on Sunday. Tropical storm conditions are possible over eastern parts of 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, the Dominican Republic, and Haiti, 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 the rest of the Dominican Republic, Haiti, the Turks and Caicos Islands, the Bahamas, Cuba, and Florida next week, but forecast uncertainty remains higher than usual. Interests in those areas should monitor the progress of Grace and updates to the forecast.

Forecast discussion by NHC Forecaster Berg.

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