a. Synoptic History
Chantal was a 60-knot
that developed just east of the Lesser Antilles, re-curved around the western
periphery of the Atlantic subtropical high pressure ridge and became
east of Newfoundland as it moved over the far north Atlantic Ocean. The
best track locations are plotted in
Fig. 1 (85K GIF)
and are listed in Table 1, along with
the one-minute maximum wind speeds and minimum central surface pressures.
Chantal originated from a tropical wave
which moved off of the coast of Africa on 5 July and soon showed signs of a
low level cloud circulation. On the 12th, satellite imagery
showed enough organization for the system to be upgraded to a
tropical depression while it was located
a few hundred miles east of the Lesser Antilles. An aircraft investigated on the
13th and confirmed the existence of a depression.
Even though there were signs of unfavorably strong upper
level westerlies, the depression strengthened to a storm on
the 14th, while centered a little over 200 n mi north-northeast
of Puerto Rico. On the 15th, it threatened the southeast and
central Bahamas as it was moving west-northwestward, but it gradually
re-curved toward the north on the 16th and 17th and did not directly affect the Bahamas.
The storm's maximum one-minute surface wind of 60 knots
is estimated to have been reached on the 17th as it was moving
northward between Bermuda and the U.S. mid Atlantic coast.
Although there was a brief threat to Bermuda, the
passed well to the west of there on the 18th. Chantal turned
toward the northeast and accelerated across the North Atlantic
shipping lanes where it became extratropical on the 20th.
b. Meteorological Statistics
Figures 2 and 3 (57K GIF)
show the minimum central surface pressure and maximum one-minute
surface wind speed curves as a function of time, along with the
data on which these curves are based. The storm was monitored by
Air Force Reserve Unit
reconnaissance aircraft from the 13th to the 18th. There were 40 penetrations
into the center of the storm during this period, which averages to one
fix every three hours. The lowest surface
pressure reported from an aircraft was 991 mb at 2338 UTC on the 16th and
the maximum wind speed was 67 knots at a flight level
of 1500 feet a few hours earlier. Table 2 lists those ship
observations for which the wind speed was near tropical storm force or higher.
c. Casualty and Damage Statistics
No reports of casualties or damage have been received in connection with Chantal.
d. Forecast and Warning Critique
The government of the Bahamas issued a
tropical storm warning
for the southeastern Bahamas and the Turks and Caicos Islands and a
tropical storm watch
for the central Bahamas at 1600 UTC 15 July. The warning was discontinued at 1200 UTC on
the 16th and the watch was discontinued three hours later.
The government of Bermuda issued a tropical storm watch at
0300 UTC on the 16th. This watch was discontinued at 1500 UTC
on the 18th. While tropical storm conditions did not
materialize for the Bahamas, the National Hurricane Center
official track forecasts on the 15th did bring the center of
the storm within about 150 n mi to the north of these islands.
The following table lists the official track forecast errors for Chantal,
along with the official track errors for the 1985-94 ten-year average:
|forecast period (hr):||0||12||24||36||48
|error (n mi):||11||47||94||152||192
|no. of cases:||(28)||(28)||(28)||(27)||(25)
The official errors for Chantal are close to the previous ten-year averages.
There was a left bias to the forecast track before re-curvature which resulted
in tropical storm warnings for the Bahamas.