page_title: Meteorological history of Hurricane Sandy
section_title: Origins
hierarchical_section_title: Meteorological history of Hurricane Sandy / Origins
caption_attribution_description: English: The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image of Sandy, as a cluster of thunderstorms, or a tropical disturbance on October 20, 2012.
context_page_description: Hurricane Sandy was the fifth-costliest Atlantic hurricane on record. It lasted for over a week in late October-early November 2012. Classified as the eighteenth named storm, tenth hurricane, and second major hurricane of the annual hurricane season, Sandy originated from a tropical wave on October 22. Performing a small loop over the central Caribbean Sea, the system intensified into a tropical storm a day later and became the final hurricane of the season before briefly coming ashore the coast of Jamaica on October 24. After emerging between Jamaica and Cuba, Sandy began a period of rapid intensification into a Category 3 hurricane on the Saffir–Simpson hurricane wind scale, with maximum sustained winds of 115 mph. It made landfall at this intensity near Santiago de Cuba on October 25.
  An approaching trough over the central United States induced high wind shear over Sandy as it traversed the Bahamas, causing the hurricane to weaken to a tropical storm while turning more northeastward. The southern part of the trough detached, causing the shear to decrease late on October 28 and allowing Sandy to regain strength.
context_section_description: The origins of Hurricane Sandy trace back to a tropical wave that moved off the western coast of Africa and into the eastern Atlantic Ocean on October 11. As the wave tracked westward over subsequent days, it interacted with an upper-level trough over the Eastern Atlantic, resulting in the development of widespread shower and thunderstorm activity; however, strong wind shear prevented further development at the time. Increased convergence, likely as a result of Hurricane Rafael to the wave's west, hindered development as well. By October 18, numerous yet disorganized convective activity formed near the center of the disturbance despite moderate wind shear. Marked with an extended low pressure area, conditions were expected to gradually become more favorable for development. On October 20, following modest organization, the National Hurricane Center (NHC) assessed a high potential for it to become a tropical cyclone within 48 hours, tagging it "Invest 99L".
  By the next day, the convection had decreased, although barometric pressures in the area remained low, a trademark of development. Convection gradually increased as the day went on, while the system slowed and became nearly stationary over the western Caribbean. By 1500 UTC on October 22, surface observations and satellite imagery indicated the system had developed enough organized convection to be classified as Tropical Depression Eighteen. At the time of the upgrade, the system was situated about 320 mi (515 km) south of Kingston, Jamaica The environment around the newly formed depression was characterized by an area of weak steering currents south of a ridge extending eastward from the Gulf of Mexico. Low wind shear and warm sea surface temperatures were conducive for strengthening, and perhaps rapid deepening. Late on October 22, a Hurricane Hunters flight observed winds of 40 mph (64 km/h) in a rainband well removed from the center of circulation, prompting the NHC to upgrade the depression to Tropical Storm Sandy. Outflow increased, while moist air helped the convection organize further. The NHC noted that "remaining nearly stationary over the warm waters of southwestern Caribbean Sea is never a good sign for this time of year." Still, the cloud pattern initially remained largely unchanged. Early on October 24, an eye began developing, as observed on microwave imagery, and Sandy was moving steadily northward, drawn by a trough approaching from the northwest. At 1500 UTC on October 24, the NHC upgraded Sandy to hurricane status after the Hurricane Hunters observed flight-level winds of 99 mph (159 km/h). At the time, Sandy was located roughly 65 mi (105 km) south of Kingston, Jamaica.
caption: Sandy as a tropical disturbance on October 20
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