Caribbean: Tropical Storm Grace tracking west-northwestwards in the Caribbean early Aug. 15 /update 3

Event

Tropical Storm Grace is tracking west-northwestwards in the Caribbean Sea early Aug. 15. As of 05:00 AST, the storm's center of circulation was approximately 100 km (60 miles) south-southeast of Saint Croix, US Virgin Islands. Forecast models indicate that the system will strengthen slightly as it continues to track in a west-northwest direction and make landfall as a tropical storm over eastern Dominican Republic early Aug. 16. After landfall, Grace will weaken slightly as it tracks west-northwestward across the Dominican Republic and northern Haiti through early Aug. 17. Grace is forecast to make another landfall over eastern Cuba afternoon Aug. 17, weaken as it continues to track northwestwards across Cuba, along the northeastern coast through late Aug. 18, and exit into the Gulf of Mexico early Aug. 19. Some uncertainty remains in the track and intensity forecast, and significant changes could occur in the coming days.

Government Advisories
As of 05:00 AST Aug. 15, the following warnings and watches are in effect:

• Tropical Storm Warning: Saba, Sint Eustatius, Sint Maarten, Saint Martin, Saint Barthelemy, US Virgin Islands, and Puerto Rico, including Vieques and Culebra as well as the Dominican Republic, from the southern Haitian border to Samana

• Tropical Storm Watch: The north coast of the Dominican Republic, from the Haitian border to Samana as well as the entire coast of Haiti

Officials could issue new warnings and/or watches in response to the developing system in the coming days.

Hazardous Conditions
The storm will likely bring heavy rainfall, strong winds, and rough seas to coastal areas of the Caribbean through at least Aug. 17. Sustained heavy rainfall could trigger flooding in low-lying communities near streams, creeks, rivers, and urban areas with easily overwhelmed stormwater drainage systems. Sites located downstream of large reservoirs could experience flash flooding after relatively short periods of intense rainfall. Forecast models indicate the system will likely bring rainfall of 7.5-15 cm (3-6 inches) to parts of the northern Leeward Islands, Virgin Islands, and Puerto Rico while Haiti and the Dominican Republic are forecast to receive 10-18 cm (4-7 inches) of rainfall through at least Aug. 17. Torrential precipitation could trigger flash floods and mudslides.

Prolonged sea swells and storm surge generated by the system may result in coastal flooding. Persistent onshore flow could make it difficult for the surge to recede and for water levels to decrease in coastal river catchments. In addition to the heavy rain, flooding, and storm surge, the storm could produce damaging wind gusts, resulting in power outages due to fallen trees and toppled utility lines.

Transport
In addition to the immediate threat to personal safety, inclement weather associated with the storm could trigger localized business, transport, and utility disruptions. Floodwaters and debris flows could render some bridges or roadways impassable, impacting overland travel in and around affected areas. Areal flooding in urban locations could also result in severe traffic congestion. Heavy rain and low visibility may trigger flight disruptions at regional airports.

Disruptions triggered by inclement weather and resultant hazards, such as flooding, could persist well after weather conditions have improved. If there is severe damage to infrastructure, repair or reconstruction efforts may exacerbate residual disruptions.

Advice

Activate contingency plans in areas where officials forecast adverse weather conditions. Heed any evacuation orders that may be issued. Use extreme caution in low-lying coastal areas and near streams, creeks, and other waterways due to the high potential for severe flooding and storm surge. Stockpile water, batteries, and other essentials in advance. Charge battery-powered devices when electricity is available; restrict the use of cellular phones to emergencies only. Power down mobile devices when not in use. Keep important documents and necessary medications in waterproof containers. Observe strict food and water precautions, as municipalities could issue boil-water advisories following flooding events. Take precautions against insect- and waterborne diseases in the coming weeks.

Plan accordingly for protracted commercial, transport, and logistics disruptions in areas in the path of the storm, especially if vital infrastructure is damaged. Seek updated information on road conditions before driving or routing shipments through areas where flooding has occurred. Confirm flights before checking out of hotels or driving to the airport; clearing passenger backlogs may take several days in some locations.

Resources

US National Hurricane Center
National Weather Service
Cuba Instituto de Meteorologia (Spanish)
Dominican Republic Oficina Nacional de Meteorologia (Spanish)
Haiti Centre national de meteorologie (French)
Meteo-France (French)