Preliminary Report
Tropical Storm Arthur
22 - 27 July 1990

1990 PRELIMINARY REPORTS

Tropical Storm Arthur (TS)
Hurricane Bertha (1)
Tropical Storm Cesar (TS)
Hurricane Diana (2)
Tropical Storm Edouard (TS)
Tropical Storm Fran (TS)
Hurricane Gustav (3)
Tropical Storm Hortense (TS)
Hurricane Isidore (2)
Hurricane Josephine (1)
Hurricane Klaus (1)
Hurricane Lili (1)
Tropical Storm Marco (TS)
Hurricane Nana (1)

a. Synoptic History

The origin of Arthur was a tropical wave that moved off the coast of Africa on 18 July. The wave consisted of a fairly concentrated area of thunderstorms centered at the low latitudes of 10°N. The wave moved westward at 17 to 23 mph. On the 22nd, near 43°W longitude, the wave was upgraded to Tropical Depression Two based on interpretation of satellite imagery.

The depression continued mostly westward with minor fluctuations in intensity and on the 24th was upgraded to Tropical Storm Arthur while centered about 250 nautical miles east of Trinidad. This was based on an Air Force reconnaissance flight as well as satellite imagery which showed an increase in convection and banding.

Arthur passed over the Windward Islands early on the 25th and its direction of motion shifted to northwestward in response to the presence of an upper-level trough over the north-central Caribbean. The also strengthened to just below hurricane force. On the 26th, it began to weaken due to an increasing vertical shear in the horizontal wind and also began to be steered by a lower portion of the vertically-averaged mean wind which caused a greater westward component of motion. It weakened to a depression on the 27th while centered about 100 nautical miles south of Hispaniola. The depression momentarily fluctuated in strength as deep convection temporarily reformed over its low-level circulation, but Air Force reconnaissance and satellite imagery indicated that the system degenerated to an open wave by late on the 27th.

b. Meteorological Statistics

In addition to the routine satellite intensity and position estimates from the Tropical Satellite and Forecast Unit, the Satellite Analysis Branch and the Air Force Global Weather Center, there were five Air Force reconnaissance missions. The first reconnaissance mission was on the 24th when the system was just east of the Windward Islands. This flight reported a maximum flight level wind speed of 47 mph just northeast of the center at an altitude of 1500 feet. A maximum surface wind of 46 mph was estimated on this same flight along with 1005 mb surface pressure. This data in combination with satellite intensity estimates were the bases for upgrading the depression to Tropical Storm Storm Arthur. Soon after, at 0000 UTC on the 25th, the ship PGDS reported a 40-mph wind speed at a location about 60 nautical miles north of the center. The storm center passed near the island of Grenada at 0800-0900 UTC and the maximum 1-minute wind speed reported there was 30 mph with a gust to 55 mph and the minimum surface pressure was 1002 mb. Winds at Trinidad and Tobago, located to the south of the center went from 340° at 3 mph to 200° at 2 mph to 150° at 14 mph as the storm center passed by to the north.

Two reconnaissance flight on the 25th, over the eastern Caribbean, indicated that Arthur quickly strengthened after passing through the islands. Flight-level winds of 81 mph and estimated surface winds of 86 mph were reported from a flight at 1450 UTC and a 78-mph flight-level wind speed was reported about 10 hours later. On the 26th, maximum reconnaissance wind speeds had decreased to 58 mph and, on the 27th, the aircraft was unable to find a closed circulation as Arthur degenerated to an open wave.

A weather radar at Crown Point, Tobago tracked Arthur as it approached the Windward Islands and provided five operational fixes of the storm center which fit quite well with satellite and reconnaissance fixes.

c. Casualty and Damage Statistics

None have been reported