Hurricane Danny was the first major hurricane to develop between the Lesser Antilles and Western Africa since Hurricane Julia in 2010. The fourth tropical cyclone, and first hurricane of the 2015 Atlantic hurricane season, Danny originated from a well-defined tropical wave that emerged over the Atlantic Ocean on August 14. Traveling west, the system gradually coalesced into a tropical depression by August 18. After becoming a tropical storm later that day, dry air slowed further development. On August 20–21, dry air became removed from the system, and Danny rapidly intensified into a Category 3 hurricane on the Saffir–Simpson hurricane wind scale. Its peak was short-lived as wind shear soon increased and prompted significant weakening. Degrading to a tropical storm by August 23, Danny approached the Lesser Antilles. It degenerated into a tropical wave as it traversed the archipelago on August 24 and was last noted over Hispaniola the following day.
The hurricane prompted the issuance of several tropical storm warnings for the Lesser Antilles. Leeward Islands Air Transport cancelled 40 flights and sandbags were distributed in the United States Virgin Islands. Danny ultimately only brought light rain to the region, with its effects considered beneficial due to a severe drought.
Meteorological history
On August 14, 2015, a well-defined tropical wave, accompanied by significant surface pressure falls, traversed Western Africa and emerged over the Atlantic Ocean that evening. A broad surface low developed along the wave on August 15. Embedded within monsoon flow, various environmental factors enabled gradual development of the disturbance, including low wind shear, above-average sea surface temperatures, moderate moisture content, and favorable diffluence. A subtropical ridge to the north steered the system generally west-northwest throughout its entire existence. On August 17, the surface low became increasingly defined and convection more persistent. It subsequently acquired enough organization to be classified a tropical depression at 06:00 UTC on August 18. At this time, it was situated about 825 mi (1,325 km) west-southwest of Praia, Cape Verde.
The depression traversed a region generally favoring further development; however, occasional intrusions of dry air from the Saharan Air Layer initially inhibited rapid growth. The system reached tropical storm-status by 12:00 UTC on August 18—based on satellite intensity estimates using the Dvorak Technique—and it was assigned the name Danny accordingly. Banding features developed around the circulation early on August 19. A temporary intrusion of dry air caused convection to collapse later that day, but cloud cover redeveloped within hours. Improving upper-level outflow supported the formation of a central dense overcast and a wide-eye soon developed. Danny reached hurricane-strength by 12:00 UTC on August 20, by which time it was located 1,095 mi (1,760 km) east of the Windward Islands. A trough over the mid-Atlantic weakened the subtropical ridge and caused the hurricane to move at a relatively slow pace of .
An unusually small hurricane, with gale-force winds extending only 60 mi (95 km) from its center, Danny was prone to significant fluctuations in intensity, making forecasts particularly difficult. Indeed, the storm soon underwent an unpredicted period of rapid intensification aided by nearly non-existent upper-level wind shear. Low-level moisture wrapped around the circulation during this phase, mitigating the influence of the Saharan air layer. Danny achieved its peak intensity around 12:00 UTC on August 21 as a Category 3 hurricane on the Saffir–Simpson hurricane wind scale; maximum sustained winds were estimated at 125 mph (205 km/h) alongside a barometric pressure of 960 mbar (hPa; ). Shortly thereafter, increasing shear and dry air initiated a rapid weakening phase. The storm's eye became obscured by clouds and disappeared from satellite image late on August 21.