10 am Advisory — Grace Grows a Little Stronger As She Heads Toward the Leeward Islands

SUMMARY OF 10:00 AM CDT INFORMATION

LOCATION…16.2N 57.9W
ABOUT 265 MI…425 KM ESE OF THE LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS…45 MPH…75 KM/H
PRESENT MOVEMENT…W OR 280 DEGREES AT 23 MPH…37 KM/H
MINIMUM CENTRAL PRESSURE…1005 MB…29.68 INCHES

WATCHES AND WARNINGS

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
* 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

FORECAST DISCUSSION

Grace is sending mixed signals on its intensity this morning. The storm has been producing persistent convective bursting since overnight, which would suggest that some strengthening has occurred. The latest subjective data-T numbers are 2.5 (35 kt) from TAFB and SAB, while objective satellite estimates are higher, roughly between 45-50 kt. Then, an ASCAT pass from 1302 UTC showed winds between 35-40 kt. Given these data, the initial intensity is set at 40 kt. A NOAA Hurricane Hunter aircraft is scheduled to investigate Grace this afternoon to provide a better estimate of the storm’s intensity.

Grace is speeding along toward the west (280 degrees) at 19 kt. Mid-level ridging, entrenched over the western Atlantic, is expected to weaken slightly during the next couple of days. This evolution should cause Grace to slow down to 10-15 kt by Sunday night and Monday and take on a west-northwestward heading. That general trajectory should continue through the end of the forecast period. The track guidance is tightly clustered during the first 48-60 hours or so, showing Grace moving near or across the Leeward Islands, Puerto Rico, and the Dominican Republic. On days 3-5, there is a little more spread, with a few models keeping the system on a southern track across Cuba while others show tracks across the Bahamas. The NHC track forecast splits this difference and continues to show a track running between Cuba and the Bahamas, very close to the HCCA consensus solution.

Deep-layer shear is forecast to be 10 kt or less for the next 36 hours or so while Grace is approaching the islands of the Greater Antilles. The thermodynamic environment also appears conducive for strengthening, but the system’s continued fast motion is likely to be an inhibiting factor on the rate of intensification. The NHC intensity forecast remains on the conservative side, bringing Grace’s intensity up to 50 kt by the time the storm reaches the Virgin Islands and Puerto Rico, but it should be noted that this forecast is on the lower side of the guidance. Only one model, the HWRF, brings Grace to hurricane strength, but it does this by having the storm move farther north and avoid land interaction altogether. The intensity forecast is highly uncertain on days 3-5 since it depends on exactly how much Grace moves over the Greater Antilles, and there is some model signal that increasing northeasterly upper-level winds over the Bahamas and Florida could become a negative factor.

KEY MESSAGES

1. Tropical storm conditions are expected in portions of the Leeward Islands tonight and early Sunday, and the Virgin Islands and Puerto Rico on Sunday. Tropical storm conditions are possible over eastern parts of the Dominican Republic by early Monday.

2. Heavy rainfall could lead to flash and urban flooding over the Leeward and Virgin Islands. Across Puerto Rico and the Dominican Republic, 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, and Florida next week, and interests in those areas should monitor the progress of Grace and updates to the forecast.

Category: ALL POSTS, Tropical