Tropical Storm Isaias Advisory 10

1. Isaias will produce heavy rains and potentially life-threatening flash flooding and mudslides across Puerto Rico, the Dominican Republic, northern Haiti, Turks and Caicos and the Bahamas. 2. Hurricane conditions and dangerous storm surge are expected in portions of the central and northwest Bahamas late Friday and Saturday. Preparations to protect life and property should be rushed to completion. Tropical storm conditions will continue to spread across portions of the Dominican Republic, Haiti, the Turks and Caicos and the southeast Bahamas tonight through Friday, and Tropical Storm Warnings are in effect for these areas. 3. Tropical storm conditions are possible along portions of the Florida east coast beginning Saturday, and a Tropical Storm Watch has been issued. While storm surge watches are not currently needed for this area, they may be required tonight or early tomorrow if the forecast track shifts closer to the coast. Heavy rains associated with Isaias may begin to affect eastern Florida this weekend, potentially resulting in isolated flash and urban flooding. 4. There is a risk of impacts from winds, heavy rainfall, and storm surge this weekend along the Florida east coast and spreading northward along the remainder of the U.S. east coast through early next week. The details of the track and intensity forecast remain uncertain and it is too soon to determine the magnitude and location of these potential impacts, but interests along the entire U.S. east coast should monitor the progress of Isaias and updates to the forecast.

CHANGES WITH THIS ADVISORY:

The government of the Bahamas has issued a Tropical Storm Warning for the northwest Bahamas.

A Tropical Storm Watch has been issued for the east coast of Florida from Ocean Reef northward to Sebastian Inlet.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
- Dominican Republic entire southern and northern coastlines
- North coast of Haiti from Le Mole St Nicholas eastward to the northern border with the Dominican Republic
- Turks and Caicos Islands
- Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayaguana, and the Ragged Islands
- Central Bahamas, including Cat Island, the Exumas, Long Island, Rum Cay, and San Salvador
- Northwestern Bahamas including Andros Island, New Providence, Eleuthera, Abacos Islands, Berry Islands, Grand Bahamas Island, and Bimini

A Tropical Storm Watch is in effect for...
- East coast of Florida from Ocean Reef to Sebastian Inlet

The Tropical Storm Warnings for the central and northwest Bahamas may be upgraded to Hurricane Warnings this evening or tonight.

Interests elsewhere along the southeast coast of the United States should monitor the progress of this system. Additional watches or warnings may be required for a portion of the Florida peninsula tonight or Friday.

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.

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.

CHANGES WITH THIS ADVISORY:

The government of the Bahamas has issued a Tropical Storm Warning for the northwest Bahamas.

A Tropical Storm Watch has been issued for the east coast of Florida from Ocean Reef northward to Sebastian Inlet.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
- Dominican Republic entire southern and northern coastlines
- North coast of Haiti from Le Mole St Nicholas eastward to the northern border with the Dominican Republic
- Turks and Caicos Islands
- Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayaguana, and the Ragged Islands
- Central Bahamas, including Cat Island, the Exumas, Long Island, Rum Cay, and San Salvador
- Northwestern Bahamas including Andros Island, New Providence, Eleuthera, Abacos Islands, Berry Islands, Grand Bahamas Island, and Bimini

A Tropical Storm Watch is in effect for...
- East coast of Florida from Ocean Reef to Sebastian Inlet

The Tropical Storm Warnings for the central and northwest Bahamas may be upgraded to Hurricane Warnings this evening or tonight.

Interests elsewhere along the southeast coast of the United States should monitor the progress of this system. Additional watches or warnings may be required for a portion of the Florida peninsula tonight or Friday.

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.

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 Isaias can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4, WMO header WTNT44 KNHC, and on the web at www.hurricanes.gov/text/MIATCDAT4.shtml. STORM SURGE: A dangerous storm surge will raise water levels by as much as 3 to 5 feet above normal tide levels in areas of onshore flow in the central and northwest Bahamas. Storm surge will raise water level by as much as 1 to 3 ft above normal tide levels in the southeastern Bahamas. WIND: Tropical storm conditions will continue to spread across portions of the Dominican Republic, Haiti, the southeastern Bahamas and Turks and Caicos within the warning area tonight. Tropical storm conditions are expected to begin in the central Bahamas Friday morning and spread into the northwestern Bahamas beginning late Friday. Hurricane conditions are expected within portions of the the central and northwestern Bahamas Friday night and Saturday. Tropical storm conditions are possible in the watch area in Florida beginning Saturday.

RAINFALL: Isaias is expected to produce the following rain accumulations: Puerto Rico, Dominican Republic and northern Haiti: 4 to 8 inches, with isolated maximum totals of 12 inches. Bahamas, Turks and Caicos: 4 to 8 inches. Cuba: 1 to 2 inches, with isolated maximum totals of 4 inches. These rainfall amounts will lead to lifethreatening flash flooding and mudslides, as well as river flooding. Urban and small stream flooding is expected for the U.S. Virgin Islands, eastern and southwestern Puerto Rico, and Hispaniola. Heavy rains associated with Isaias may begin to affect eastern Florida over the weekend. This rain could result in isolated flash and urban flooding, especially in lowlying and poorly drained areas.

SURF: Swells generated by Isaias are affecting portions of the Leeward Islands, the Virgin Islands, Puerto Rico, the Dominican Republic, the Turks and Caicos Islands and the southeastern Bahamas. These swells will spread along the coast of Cuba and into the central and northwestern Bahamas over the next day or two. These swells are likely to cause lifethreatening surf and rip current conditions. Please consult products from your local weather office.

Key messages for Isaias can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4, WMO header WTNT44 KNHC, and on the web at www.hurricanes.gov/text/MIATCDAT4.shtml. STORM SURGE: A dangerous storm surge will raise water levels by as much as 3 to 5 feet above normal tide levels in areas of onshore flow in the central and northwest Bahamas. Storm surge will raise water level by as much as 1 to 3 ft above normal tide levels in the southeastern Bahamas. WIND: Tropical storm conditions will continue to spread across portions of the Dominican Republic, Haiti, the southeastern Bahamas and Turks and Caicos within the warning area tonight. Tropical storm conditions are expected to begin in the central Bahamas Friday morning and spread into the northwestern Bahamas beginning late Friday. Hurricane conditions are expected within portions of the the central and northwestern Bahamas Friday night and Saturday. Tropical storm conditions are possible in the watch area in Florida beginning Saturday.

RAINFALL: Isaias is expected to produce the following rain accumulations: Puerto Rico, Dominican Republic and northern Haiti: 4 to 8 inches, with isolated maximum totals of 12 inches. Bahamas, Turks and Caicos: 4 to 8 inches. Cuba: 1 to 2 inches, with isolated maximum totals of 4 inches. These rainfall amounts will lead to lifethreatening flash flooding and mudslides, as well as river flooding. Urban and small stream flooding is expected for the U.S. Virgin Islands, eastern and southwestern Puerto Rico, and Hispaniola. Heavy rains associated with Isaias may begin to affect eastern Florida over the weekend. This rain could result in isolated flash and urban flooding, especially in lowlying and poorly drained areas.

SURF: Swells generated by Isaias are affecting portions of the Leeward Islands, the Virgin Islands, Puerto Rico, the Dominican Republic, the Turks and Caicos Islands and the southeastern Bahamas. These swells will spread along the coast of Cuba and into the central and northwestern Bahamas over the next day or two. These swells are likely to cause lifethreatening surf and rip current conditions. Please consult products from your local weather office.

At 500 PM EDT (2100 UTC), the center of Tropical Storm Isaias was located near latitude 19.5 North, longitude 70.6 West. Isaias is moving toward the northwest near 20 mph (31 km/h) and a northwestward motion with some decrease in forward speed is expected over the next couple of days. On the forecast track, the center of Isaias will move near the Southeastern Bahamas by late tonight. Isaias is forecast to be near the Central Bahamas Friday night and move near or over the Northwest Bahamas and near South Florida on Saturday.

Maximum sustained winds are near 60 mph (95 km/h) with higher gusts. Strengthening is forecast during the next day or so, and Isaias is forecast to become a hurricane on Friday or Friday night.

Tropicalstormforce winds extend outward up to 240 miles (390 km) from the center.

The estimated minimum central pressure based on surface observations in the Dominican Republic is 999 mb (29.50 inches).

At 500 PM EDT (2100 UTC), the center of Tropical Storm Isaias was located near latitude 19.5 North, longitude 70.6 West. Isaias is moving toward the northwest near 20 mph (31 km/h) and a northwestward motion with some decrease in forward speed is expected over the next couple of days. On the forecast track, the center of Isaias will move near the Southeastern Bahamas by late tonight. Isaias is forecast to be near the Central Bahamas Friday night and move near or over the Northwest Bahamas and near South Florida on Saturday.

Maximum sustained winds are near 60 mph (95 km/h) with higher gusts. Strengthening is forecast during the next day or so, and Isaias is forecast to become a hurricane on Friday or Friday night.

Tropicalstormforce winds extend outward up to 240 miles (390 km) from the center.

The estimated minimum central pressure based on surface observations in the Dominican Republic is 999 mb (29.50 inches).

Surface observations in the Dominican Republic indicate that the poorly defined center of Isaias moved over the southeastern portion of Hispaniola around 1600 UTC. There is currently a significant concentration of convection near the mid-level center that is located along the northern coast of the island, and recent surface observations suggest that a new center may be forming near the area of mid-level rotation seen in satellite imagery. The advisory position has been placed between the previous estimated center location and the mid-level center until it becomes more clear that reformation has occurred. Earlier ASCAT data that arrived shortly after the previous advisory and reconnaissance aircraft data from this morning supported an intensity of 45-50 kt, and since there has no significant degradation the overall organization since that time, the initial intensity remains 50 kt. The central pressure of 999 mb is based on a surface observation of 1001 mb and 25 kt of wind at Puerto Plata in the Dominican Republic.

The initial motion estimate is a somewhat uncertain 310/17 kt. The track forecast reasoning has not changed since the previous advisory. The tropical storm should continue on a general northwest heading during the next 24 to 36 hours along the southern side of a subtropical ridge. After that time, a trough moving into the east-central United States should cause Isaias to turn north-northwestward and northward as the western portion of the ridge erodes. By early next week, Isaias is expected to turn northeastward and accelerate ahead of the aforementioned trough. The 1200 UTC dynamical model guidance has shifted eastward and now that Isaias is expected to become a stronger and deeper cyclone, that also favors a more eastward track. The updated official forecast is a blend of the various consensus aids. Since the new center is still in its formative stage some additional shifts in the track may occur. In addition, strong winds and heavy rainfall will extend far from the center.

Visible imagery has shown significant banding near the mid-level circulation. Assuming that the center reforms near that feature and moves away from Hispaniola tonight, strengthening is expected during the next 24-36 hours and Isaias is now forecast to become a hurricane. After that time, there are mixed signals regarding the amount of southwesterly vertical wind shear and the models generally do not show much additional strengthening. Therefore, the NHC intensity forecast shows a leveling off in intensity after 48 h. It still needs to be stressed that that there is a higher than usual amount of uncertainty in the intensity forecast.

Surface observations in the Dominican Republic indicate that the poorly defined center of Isaias moved over the southeastern portion of Hispaniola around 1600 UTC. There is currently a significant concentration of convection near the mid-level center that is located along the northern coast of the island, and recent surface observations suggest that a new center may be forming near the area of mid-level rotation seen in satellite imagery. The advisory position has been placed between the previous estimated center location and the mid-level center until it becomes more clear that reformation has occurred. Earlier ASCAT data that arrived shortly after the previous advisory and reconnaissance aircraft data from this morning supported an intensity of 45-50 kt, and since there has no significant degradation the overall organization since that time, the initial intensity remains 50 kt. The central pressure of 999 mb is based on a surface observation of 1001 mb and 25 kt of wind at Puerto Plata in the Dominican Republic.

The initial motion estimate is a somewhat uncertain 310/17 kt. The track forecast reasoning has not changed since the previous advisory. The tropical storm should continue on a general northwest heading during the next 24 to 36 hours along the southern side of a subtropical ridge. After that time, a trough moving into the east-central United States should cause Isaias to turn north-northwestward and northward as the western portion of the ridge erodes. By early next week, Isaias is expected to turn northeastward and accelerate ahead of the aforementioned trough. The 1200 UTC dynamical model guidance has shifted eastward and now that Isaias is expected to become a stronger and deeper cyclone, that also favors a more eastward track. The updated official forecast is a blend of the various consensus aids. Since the new center is still in its formative stage some additional shifts in the track may occur. In addition, strong winds and heavy rainfall will extend far from the center.

Visible imagery has shown significant banding near the mid-level circulation. Assuming that the center reforms near that feature and moves away from Hispaniola tonight, strengthening is expected during the next 24-36 hours and Isaias is now forecast to become a hurricane. After that time, there are mixed signals regarding the amount of southwesterly vertical wind shear and the models generally do not show much additional strengthening. Therefore, the NHC intensity forecast shows a leveling off in intensity after 48 h. It still needs to be stressed that that there is a higher than usual amount of uncertainty in the intensity forecast.

al092020 Tropical Storm Isaias