Hurricane Nana 1990

Preliminary Report
Hurricane Nana
16 - 21 October 1990


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)

Nana makes 1990 the most active season since 1969.


a. Synoptic History

The 14th named system of the 1990 Atlantic season developed from a vigorous tropical wave which moved over the cape Verde Islands on 7 October. Surface and upper-air data from the islands revealed that the wave produced squalls and a marked 52-mph wind shift at the low levels. Data also indicated that the upper-level conditions were not favourable for development, since the westerlies were already establieshed in that region. The wave travelled westward for the next several days in tandem with a broad upper-level trough to its west and maintained deep but disorganised convection.

On 13 October, the wave reached the Lesser Antilles and its northern portion moved northwestward while the southern sector continued westward through the Caribbean. The northern portion of the wave became convectively active in the vicinity of high-level divergence provided by a deepening upper level trough.

The convection became organized as the trough moved out of the area and the shear relaxed. Finally, on 16 October, satellite images and data from an Air Force plane indicated that a tropical depression had developed about 360 nautical miles northeast of Puerto Rico. The depression intensified rapidly and at 1800 UTC 17 October the system had already reached hurricane status.

Nana moved toward the north-northwest track and became a threat to Bermuda. However, the threat was short lived because a new impulse of upper level westerlies moved across the hurricane and seperated the convection from its low-level center. Consequently, Nana weakened to a tropical depression and drifted in a southerly direction, steered by the low level flow until it dissipated at 1800 UTC 21 October. The remnants of Nana were depicted on satellite images for the next few days as a westward moving swirl of low clouds with transient convection.

b. Meteorological Statistics

Nana was a very small hurricane. During a flight on 18 October when Nana was still on developing stage the Air Force plane reported a closed 8 nautical mile diameter eyewall and estimated surface winds of 109 mph in a very small area north of the eye. The Air Force crew reported textually " surface pressure dropped like a rock at the time we exited the eye " at 1146 UTC 18 October when Nana was still in a developing stage. The reported winds were stronger than would be expected for a system with the measure minimum pressure. However, those reports and the comments from the crew were the primary basis for classifying Nana as a hurricane.

The vessel USNS Sealift Med. reported sustained southerly winds of 69 mph while located about 120 nautical miles southeast of the center at 1200 UTC 18 October. An Analysis of the surrounding data indicated that the ship observation was probably an error or perhaps the ship was was in a squall at that time.

c. Casualty and Damage Statistics

None have been reported.

Maximum Intensity For Hurricane Nana
16 - 21 October, 1990

Position Pressure
Wind Speed
Lat. (°N) Lon. (°W)
19/1200 28.5 66.9 989 85 Category 1 Hurricane