a. Synoptic History
A weak low-level circulation developed within a cluster of thunderstorms over the Florida
Straits on 29 May 1997. The poorly organized system drifted northeastward over the next two days
with little development. The system accelerated north-northeastward late on 31 May. Surface reports
then indicated a low pressure area without a well-defined closed circulation, although 20-25 kt winds
were occurring east of the low. A shortwave trough approaching from the southwest enhanced
convection near the system center, and a post-analysis of satellite and
surface observations suggests that the system became a subtropical depression
at 0600 UTC 1 June (Table 1 and
Figure 1 [19K GIF]).
The depression moved rapidly north-northeastward and strengthened. It reached
subtropical storm strength at 1200 UTC 1 June and a peak intensity of
45 kt 6 h later. Satellite imagery on the 1st showed a well-defined low-level
center with a band of relatively shallow cumulonimbus wrapped around the south side of the center. The
cyclone turned east-northeastward on 2 June when
located about 120 nm south of the New England coast. It became extratropical
around 1800 UTC that day and merged with a cold front. The remnant low dissipated by 0000 UTC 3 June.
b. Meteorological Statistics
Figures 2 (14K GIF) and
3 (14K GIF) show
best track curves of minimum central pressure and maximum
one-minute surface wind speed, respectively, as a function of time. The curves are based primarily on
Hebert-Poteat estimates from satellite imagery, augmented by surface and
NOAA data buoy 41002 reported a minimum pressure of
1003.8 mb with a coincident 8.5 minute average wind of 27 kt and gusts to 35 kt at 1000 UTC 1 June. A
10-minute average wind of 32 kt occurred between 1000 and 1100 UTC. An Air Force
a minimum pressure of 1004 mb at 1930 UTC 1 June, with maximum flight level winds of 55 kt at
1500 ft. No other reports of tropical-storm force winds were received at the NHC.
c. Casualty and Damage Statistics
No reports of damage or casualties associated with the subtropical storm have been received
at the NHC.
d. Forecast and Warning Critique
NHC wrote no advisories on this system, so there are no official forecasts to verify.
Operationally, analysis and forecast information on the system was provided in the
National Weather Service Offshore Waters Forecasts,
where it was considered to be an extratropical gale. This approach was agreed to during conference
calls on the morning and afternoon of 1 June between the NHC, U.S. Navy,
Hydrometeorological Prediction Center and appropriate NWS
offices with marine responsibility. Sufficient information on this system was available in real time
within routine NWS marine products. This post-storm analysis concludes that this non-frontal system
should be designated as subtropical for purposes of historical record
keeping because it had a relatively tight circulation as indicated by aircraft data and organized
convection near the circulation center, but there was insufficient evidence of a warm-core circulation
to justify classifying the system as a tropical storm.
NHC track prediction guidance correctly indicated the general north-northeastward motion
followed by an eastward turn before the storm reached New England. However, no meaningful
model verification statistics are available.