Hurricane Dora (1999) - Meteorological History

Meteorological History

A tropical wave emerged into the Atlantic Ocean from the west coast of Africa on July 23. It tracked through the Atlantic and Caribbean Sea for several days with minimal development. By August 4, the system entered the Pacific Ocean, accompanied by disorganized convection. During the next 24 hours, satellite imagery noted evidence of a low-level circulation, as well as the formation of curved convective banding. As a result, it is estimated that Tropical Depression Seven-E developed at 0000 UTC on August 6, while located about 335 miles (540 km) south of Acapulco. Three hours later, the National Hurricane Center began issuing advisories on the depression and forecasted significant intensification. Despite initial vertical wind shear, the depression steadily intensified and was upgraded to Tropical Storm Dora later that day. Upon becoming a tropical storm, the National Hurricane Center noted "there would seem to be no reason why Dora should not strengthen", citing decent outflow on the western side of the storm and SST's of nearly 84 °F (29 °C). Tracking west-northwestward and then westward, Dora continued to strengthen and was upgraded to a hurricane on August 8.

Moving westward along a decaying subtropical ridge, Dora steadily increased to hurricane status on August 8, based on estimates through the Dvořák technique. Weak wind shear ahead of the storm and warm waters allowed continued strengthening as a small, well-defined eye formed. On August 12, Dora reached its peak intensity of 140 mph (220 km/h) as the barometric pressure dropped to a minimum of 943 mbar. Shortly after its peak intensity, Dora underwent an eyewall replacement cycle, resulting in a brief weakening before again restrengthening to winds of 140 mph (220 km/h) late on August 13. Dora never strengthened any further as the storm encountered cooler waters and light wind shear.

Subsequent to peaking in intensity, Dora encountered cooler waters and increased wind shear. On August 14 it crossed into the central Pacific Ocean as a Category 2 hurricane on the Saffir-Simpson Hurricane Scale; the duty of hurricane warnings were transferred from the National Hurricane Center to the Central Pacific Hurricane Center. Dora again encountered favorable conditions, and on August 15 re-intensified to major hurricane status as it passed 200 miles (320 km) south of Big Island, Hawaii. The secondary peak intensity was brief, as weakening occurred after the forward speed increased. Dora passed 65 miles (105 km) south of Johnston Island on August 18 before turning west-northwest, and on August 19 it crossed the International Date Line as a 70 mph (115 km/h) tropical storm; the Joint Typhoon Warning Center tracked the remainder of the duration of Dora. The storm encountered stronger wind shear, and by August 21 winds decreased to below tropical storm force. On August 23, the circulation became exposed from the main convection, and at 1800 UTC Tropical Depression Dora dissipated about 450 miles (725 km) northeast of Wake Island.