Hurricane Cosme (2007)

Map plotting the storm's track and intensity, according to the Saffir–Simpson scale

Map key

Saffir–Simpson scale

  Tropical depression (≤38 mph, ≤62 km/h)
  Tropical storm (39–73 mph, 63–118 km/h)
  Category 1 (74–95 mph, 119–153 km/h)
  Category 2 (96–110 mph, 154–177 km/h)
  Category 3 (111–129 mph, 178–208 km/h)
  Category 4 (130–156 mph, 209–251 km/h)
  Category 5 (≥157 mph, ≥252 km/h)
  Unknown

Storm type

Tropical cyclone

Subtropical cyclone

Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression

The origins of Cosme can be traced back to a tropical wave that left the coast of Africa on June 27, 2007. Due to a lack of associated convection, the wave was difficult to track across the Atlantic Ocean and Caribbean Sea. The National Hurricane Center (NHC) estimated that the wave emerged into the Pacific Ocean on July 8. Because the system was embedded within the Intertropical Convergence Zone (ITCZ), development was initially slow. However, when it separated from the ITCZ on July 13, the disturbance increased in convective organization, and was classified as Tropical Depression Six-E about midway between Mexico and Hawaii.[1] It tracked westward at 12 mph (19 km/h) due to steering currents of a tropical easterly flow. Although wind shear was generally light, ocean temperatures were only marginal for tropical cyclone intensification.[2][3] Forecasters experienced difficulty in locating the exact center of circulation. By July 14, convection had steadily decreased,[4] although the storm's movement was initially uncertain due to its location within a broad low pressure area.[5] Early on July 15 the depression's appearance on satellite imagery improved,[6] and at 1800 UTC the NHC upgraded the depression to tropical storm status, and gave it the name "Cosme".[1]

Shortly after attaining tropical storm status, the previously broad circulation consolidated as banding features developed.[7] The inner core gradually condensed and tightened, as indicated by an AMSR-E overpass.[8] On July 16 an eye began to form and Cosme intensified to attain winds of 65 mph (105 km/h). Tracking northwest towards a weakness in the mid-level ridge,[9] the cyclone continued to intensify and was upgraded to Hurricane Cosme late on July 16, about 1,600 mi (2,600 km) east of Hilo.[1] The hurricane reached peak intensity with winds of 75 mph (120 km/h), although due to cooler waters it quickly weakened to a tropical storm,[1] as the eye became ragged and cloud-filled.[10]

By July 17, the cloud pattern had deteriorated, and its winds decreased to 45 mph (75 km/h).[11] The center subsequently became exposed, with just a few thunderstorms confined to the southwest portion of the storm as it began to accelerate to the west.[12] As easterly vertical wind shear increased, convection temporarily reformed in a concentrated area southwest of the center.[13] As Cosme reached steadily cooler water temperatures, it was downgraded to a tropical depression late on July 18 about 900 mi (1,400 km) southeast of Hilo, Hawaii; at around the same time, the storm entered the forecast responsibility of the Central Pacific Hurricane Center.[1] Tracking westward at 14 mph (23 km/h), maximum sustained winds were 35 mph (56 km/h) with localized higher gusts.[14] Gradually weakening, Tropical Depression Cosme passed south of the Hawaiian Islands on July 20 with a minimum central pressure of 1010 mbar.[15] On July 22, the depression came within 180 mi (290 km) of Johnston Island,[16] and later that day, it degenerated into a remnant low.[1]

Tropical Storm Cosme near hurricane intensity on July 16

Initially, Cosme was predicted to make landfall on Hawaii as a tropical storm.[17] In anticipation of the storm, the National Weather Service issued a flash flood watch for the island of Hawaii on July 20. Also, small craft advisories were in effect for Maui and Hawaii;[18] wind advisories were issued for summits in those regions.[19] High surf advisories were also put into effect for coastal areas.[20] The Hawaii County Civil Defense prepared for the storm by planning for increases in emergency response personnel and opening of evacuation centers.[21] County crews worked to clean out drains and culverts to prevent flooding.[20]

Because the depression stayed far from land, the effects were mostly minor and little damage was reported.[1] A strong trade wind swell north of Cosme generated waves up to 9 ft (2.7 m) high.[22] Rain bands produced up to 6.94 in (176 mm) of rainfall,[23] causing small stream and drainage ditch flooding, as well as ponding on roadways in portions of Hilo, Puna, and Kau.[24] The rainfall helped to relieve a persistent drought which had existed for several months.[25] Wind gusts reached 40 mph (65 km/h) in southern portions of Hawaii, causing no known damage.[25]

• List of Hawaii hurricanes
• Other tropical cyclones named Cosme
• Timeline of the 2007 Pacific hurricane season