Grace (2015)

A westward-moving tropical wave that left the coast of western Africa on September 3 developed a tighter circulation and became a tropical depression around 0600 UTC on September 5 about 150 nautical miles south of Cabo Verde. It strengthened to Tropical Storm Grace by 1800 UTC that day, moved generally westward across the eastern Atlantic, reached peak intensity on September 6, then weakened as it encountered cooler waters and dry air and degenerated to a trough by 1200 UTC September 9 about 650 nautical miles east of the Lesser Antilles.

There were no landfalls associated with Grace. After degeneration, the remnants produced gusty winds and heavy rains over the northeastern Leeward Islands and Puerto Rico a couple of days later, but Grace did not make landfall as a tropical cyclone and no watches or warnings were issued.

Grace’s maximum intensity was estimated at 50 knots (about 58 mph) with a minimum central pressure of 1000 mb near 1200 UTC on September 6. That peak corresponds to a moderate tropical storm (below hurricane strength).

Reported storm surge and rainfall impacts were limited. The NHC report notes that the remnants brought heavy rainfall and gusty winds to the northeastern Leeward Islands and Puerto Rico, but there were no specific storm surge measurements or large rainfall totals tied directly to Grace listed in the report, and no ship or land-based observations of tropical-storm-force winds were recorded.

There were no reports of damage or casualties attributed to Grace. The most affected areas from the remnants were the northeastern Leeward Islands and Puerto Rico where gusty winds and heavy rain occurred, but no confirmed injuries, deaths, or structural damage were reported.

Notable points: genesis forecasts for the system had mixed skill—Grace was included early in outlooks but was briefly removed and the high probability of formation was only issued about 6 hours before genesis. NHC track forecasts were generally better than the recent average and compared well with most guidance, while intensity forecasts had a high bias after 24 hours and several guidance models outperformed the official intensity forecasts.