Hurricane Dora (1999)

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 00:00 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 ocean temperatures of nearly 84 °F (29 °C). Although the center began difficult to locate on satellite imagery on August 7, Dvorak T-numbers did not indicate a decrease in intensity. Tracking west-northwestward and then westward along a decaying subtropical ridge, Dora continued to intensify and was upgraded to a hurricane on August 8 based on the Dvorak technique.

Late on August 8, the storm consisted primarily of central dense overcast, but minimal banding features. At 00:00 UTC on August 9, Dora intensified into a Category 2 hurricane. Several hours later, an eye with a diameter of about 6–12 mi (10–19 km) developed, and the cyclone organized further. Thus, it was predicted that Dora would soon reach Category 3 intensity. The storm strengthened into a Category 3 hurricane around 00:00 UTC on August 10. In a forecast discussion by the National Hurricane Center nine hours later, it was noted that a mid-troposhperic ridge would track eastward, thus causing Dora to move in a west-northwestward motion. However, the hurricane instead continued westward or slightly north of due west. Late on August 10, deep convection significantly expanded and became more symmetric, while Dvorak intensity estimates indicated that Dora reached Category 4 intensity. A predicted weakening trend led the National Hurricane Center to note that Dora was likely near peak intensity.

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.

Impact and records

On August 16, forecast models predicted Dora would bypass Johnston Island a short distance to the south, with some concerns of a direct hit on the island. As a result of the threat, about 1,200 workers and residents evacuated Johnston Atoll to Hawaii. Prior to leaving, workers secured construction equipment and other loose items. Some biologists on Johnston Atoll were concerned that the hurricane would severely impact the reproductive cycle of over 150,000 birds in the Johnston Atoll Wildlife Refuge, a concern expressed after Hurricane John in 1994 killed 80% of the bird population during its impact on Johnston Atoll. Additionally, the Central Pacific Hurricane Center predicted Dora would strike Wake Island as a minimal typhoon, though it did not occur.

An ocean swell from Dora produced 8 – 20 foot (2 – 6 m) waves along the east and southern shores of the island of Hawaii. This prompted local officials to close all beaches, campsites and nature trails in the Puna and Kau districts due to the deteriorating conditions. The outer rainbands produced winds of up to 60 mph (95 km/h) at some high elevations, and also resulted in some light rainfall. Hurricane Dora also produced rough surf on Johnston Island, with one forecaster remarking the surf was the most severe aspect of the storm. The automatic station at Johnston Atoll reported wind gusts between 40 — 45 mph (75 – 85 km/h) for two hours. Overall effects were minimal, and there were no reports of damage or injuries.

With a total track of 6,500 miles (10,500 km), Hurricane Dora had the second longest track of a Pacific hurricane, behind only Hurricane John of 1994; the length of the track of Dora was more than four times the basin average. Dora was also the first Pacific hurricane to come close enough to be detected by radar. In addition, the hurricane was the first tropical cyclone to move across all three Pacific basins since John in 1994.