Caribbean Sea: Tropical Depression Grace tracking westward over southern Haiti late Aug. 16 /update 6

Event

Tropical Depression Grace is tracking westward over southern Haiti late Aug. 16. As of 23:00 AST, the storm's center of circulation was approximately 165 km (100 miles) west-southwest of Port-au-Prince. Forecast models indicate the system will strengthen slightly and turn into a tropical storm by early Aug. 17. Grace is forecast to turn to track west-northwestwards and pass between Jamaica and Cuba Aug. 17 and between Grand Cayman and Little Cayman of the Cayman Islands early Aug. 18. The system will likely make landfall as a tropical storm north of Playa del Carmen, Quintana Roo State, Mexico, early Aug. 19. Grace is forecast to enter the Gulf of Mexico later the same day and strengthen into a typhoon by late Aug. 20. The storm will likely make another landfall as a typhoon over Tampico-Altamira in Tamaulipas State, Mexico, early Aug. 21. Some uncertainty remains in the track and intensity forecast, and significant changes could occur in the coming days.

Government Advisories
As of 23:00 AST Aug. 16, the following warnings and watches are in effect:

• Tropical Storm Warning: The southern coast of the Cuban provinces of Santiago de Cuba, Granma, Las Tunas, and Camaguey; Cayman Islands.

• Tropical Storm Watch: The entire coast of Haiti; Jamaica; the southern coast of the Cuban provinces of Ciego de Avila, Sancti Spiritus, Cienfuegos, Matanzas, and Pinar del Rio as well as Isla de la Juventud.

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 13-25 cm (5-10 inches) in Haiti and the Dominican Republic through Aug. 17. Over southern Cuba, Jamaica, and the Cayman Islands, forecasts indicate that 5-10 cm (2-4 inches) of rain through Aug. 19. The northern Yucatan Peninsula is forecast to receive 7.5-15 cm (3-6 inches) of rain Aug. 18-19. Torrential precipitation could trigger flash floods and mudslides. Severe weather conditions are also likely to complicate ongoing rescue and relief efforts in the Tiburon Peninsula, Haiti; a magnitude-7.2 earthquake Aug. 14 killed around 1,300 people and resulted in widespread infrastructural damage and utility disruptions.

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. Swells due to Grace are forecast to affect portions of Hispaniola through Aug. 17 and spread westward to Jamaica, the Cayman Islands, the southern coast of Cuba, and the Yucatan Peninsula of Mexico after Aug. 17. 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)