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Tropical Storm Grace was a tropical cyclone that formed at 41.2N just north of the Azores. As a tropical cyclone, it did not affect land. It moved north-east and finally turned to the east and dissipated. Its remnants affected parts of the United Kingdom, Ireland, France and Portugal.
Tropical Storm Grace originated from a large extratropical cyclone that formed along a cold fronton September 27, 2009 roughly 470 mi (755 km) east of Cape Race, Newfoundland. Initially attached to an occluded front, the low detached from the system and gradually acquired sometropical characteristics. By October 1, convection began to develop near the center of the system as it tracked through the central Azores. The following day, convection began to decrease around the low and the National Hurricane Center (NHC) ceased monitoring it. Over the following two days, the system executed a counter-clockwise loop near the Azores. During the afternoon of October 4, convection redeveloped around the center of the low and was classified as a tropical storm near São Miguel Island. Although the storm was tropical at this time, the NHC did not issue advisories for several hours.
The first advisory from the NHC was issued at 11:00 AST on October 4; at this time, the system was officially named Grace, the seventh named storm of the 2009 Atlantic hurricane season. The storm featured relatively deep convection around an eye-like feature. Although Grace was over waters normally not warm enough for tropical cyclone development, low wind shear allowed the convection to persist. A steady northeastward track was taken by the storm in response to a southerly flow over the northwestern Atlantic. The storm intensified slightly as it moved over decreasing sea surface temperatures, with winds estimated at 70 mph (110 km/h) early on October 5. However, in a post-storm analysis from the NHC, it was found that Grace attained peak winds of 65 mph (100 km/h), slightly lower than operationally stated. Around this time, the storm was estimated to have had a 9% chance of intensifying to Category 1 intensity on the Saffir–Simpson Hurricane Scale.
A large extratropical cyclone near Grace caused the storm to deteriorate, with convection weakening and becoming asymmetric. By this time, the storm was over 18 °C (64 °F) waters, likely inhibiting convective development. Shower and thunderstorm activity continued to diminish throughout the day on October 5; however, Grace maintained tropical characteristics, namely a deep, warm core. Early on October 6, the NHC issued their final advisory on Grace as it merged with a frontal system over the northeastern Atlantic. Just prior to merging, the lowest pressure in relation to the storm was recorded at 986 mbar (hPa; 29.12 inHg) The extratropical remnants of Grace persisted for roughly 18 hours before dissipating over theCeltic Sea early on October 7. However, the United States Naval Research Laboratory continued to monitor the system for several more hours until it moved over the North Sea.
Although officially designated a tropical cyclone by the NHC, Météo-France, the French meteorological service, stated in their annual report to the World Meteorological Organization that Grace should not have been classified a tropical system. In their report, they argued that although the storm presented deep convection, an eye-like feature, and winds above 60 mph (95 km/h), the overall development of Grace was more similar to that of a mid-latitude non-tropical cyclone. However, operationally, Météo-France considered Grace to be a subtropical cyclone. They also criticized the NHC of warning upon this system based on recent trends of the link between global warming and increased hurricane activity.