Hortense became the second category four hurricane
and the fourth category three hurricane on the Saffir-Simpson Hurricane
Scale (SSHS) of the season. Hortense was a wet hurricane and
most of the damage was caused by its accompanying torrential
rains. Hortense crossed the southwestern tip of Puerto Rico and
the eastern top of the Dominican Republic as a category one
hurricane and the associated floods killed at least 21 people.
Hortense moved northward over the western Atlantic and crossed
Nova Scotia as a weakening hurricane.
a. Synoptic History
A broad area of low-pressure associated with a
crossed Dakar, Africa on 30 August. The Dakar vertical-time
section during that period showed a well marked cyclonic wind
shift below 700 mb and a 55-knot easterly jet at 550 mb. Surface
observations indicated that a 1005 mb low associated with the wave
moved just south of the Cape Verde Islands on the 31st. Although
the system had a well defined low- to middle- level circulation,
satellite images indicated that the deep convection was minimal.
The low-pressure area continued moving westward and during 3
September, it crossed an array of
NOAA drifting buoys.
Data from these buoys helped to determine that the system had become a
at 1200 UTC 3 September (Fig 1 [44K GIF]).
The depression continued almost due westward around the
periphery of a strong high pressure ridge with no significant
change in strength. Satellite images suggest that for the next
couple of days, deep convection was rather intermittent and not
well organized. In fact, on 6 September, the first reconnaissance
flight into the system found a broad circulation and only a few
squalls. As the depression approached the Lesser Antilles, upper-
level winds became more favorable for strengthening and satellite
images showed an increase in deep, organized convection. It is
estimated that the depression reached tropical storm
status at 0600 UTC 7 September. An early reconnaissance flight on that day
reported peak winds of 62 knots at flight level and a minimum
pressure of 1001 mb confirming the strengthening of the system.
Hortense moved over Guadeloupe, where the pressure dropped to
998 mb and produced sustained winds of 46 knots with gusts to
70 knots. It also produced torrential rains. The
moved westward into the eastern Caribbean and encountered a fast
eastward moving upper-level short wave. This increased the
vertical wind shear which temporarily inhibited strengthening. In
fact, high resolution visible satellite images clearly showed that
the low-level center
of the tropical cyclone became exposed during
the morning of the 8th. A new burst of deep convection developed
over the center later in the afternoon and a gradual
intensification began. By then, the short-wave had moved out of the
area and the shear had relaxed. Hortense became a hurricane at
0600 UTC 9 September.
After slowing down just to the south southeast of Puerto Rico,
Hortense took a jog toward the northwest and the center moved over
southwestern Puerto Rico. Fixes from the
San Juan WSR-88D radar
indicate that the eyewall
of Hortense reached the coast near Guanica about 0600 UTC on the 10th
and moved over the southwestern tip of the island for about 2 hours.
Hortense moved through the Mona Passage and weakened slightly
while the circulation was interacting with land. The center passed
very close to Punta Cana, on the eastern tip of Dominican Republic
where a calm was felt and the pressure dropped to 988 mb. The
hurricane continued on a northwesterly track and the center moved
just east of the Turks and Caicos Islands. Hurricane conditions
were observed in some of these islands. Thereafter, Hortense
briefly reached category four status with a peak intensity of 120
knots and 935 mb minimum pressure at 0000 UTC 13 September.
A developing trough along the eastern United States forced the
hurricane to turn northward with an increase in forward speed. A
weakened Hurricane Hortense rapidly crossed eastern Nova Scotia on 15 September and
while moving just south of Newfoundland later on that day.
Hortense's track is shown in
Fig. 2 (73K GIF).
Table 1 is a listing, at six-hour intervals, of the
position, estimated minimum central pressure and maximum 1-minute surface wind speed.
b. Meteorological Statistics
The best track pressure and wind curves as a function of time are shown in
Fig. 3 (31K GIF) and
4 (27K GIF)
and are based on reconnaissance and surface observations,
satellite intensity estimates from the
Tropical Analysis and Forecast Branch
(TAFB) of the Tropical Prediction Center. It also includes estimates from the
Satellite Analysis Branch (SAB) and the
Air Force Global Weather Central (AFGWC).
Hortense was a wet hurricane. It produced about 10 inches of
rain in Guadeloupe and dumped between 15 and 20 inches of rain over
Puerto Rico and the U.S. Virgin Islands with possibly higher
amounts in the mountains. Rainfall distribution associated with Hortense is displayed in
Fig. 5 (120K GIF). The Dominican Republic
also experienced torrential rains with a maximum of 19.25 inches in the
town of San Rafael de Yuma.
There are unconfirmed reports of gusts to 95 knots in the
southwestern tip of Puerto Rico about 0800 UTC 10 September. These
strong winds may have been a local effect caused by the Venturi
effect (acceleration between walls). Residents of the southwestern
portion of Puerto Rico reported calm winds and that the "stars were
out" as the eye
crossed the area. Peak winds of hurricane force
were reported over the Dominican Republic, and hurricane force
winds were registered in Grand Turk and Nova Scotia. Tables 2
and 3 contain selected surface observations and ships reporting
34-knot winds or higher associated with Hortense.
Hortense was upgraded to a category four hurricane of 120 knots
based on a report from a
plane of 123 knots at 700 mb in the northeast quadrant at 2130 UTC followed
by 128 knots in the southeast quadrant at 2220 UTC. The plane also
reported a minimum pressure of 935 mb, a closed eyewall of 11 n mi
in diameter and an excellent stadium (outward slope of the
convective clouds in the eyewall) effect at 2323 UTC. In addition,
satellite objective T-numbers were of the order of 6.5 on the
Dvorak scale, corresponding to an intensity 127 knots and a
pressure of 935 mb. Visible satellite images revealed a spectacular
cloud pattern with a clearly distinct eye during that time.
c. Casualty and Damage Statistics
Hortense devastated portions of Puerto Rico but most of the damage was not
done by winds or storm surge.
Instead, torrential rains produced flash floods and mud slides which killed at least 18
people. A preliminary report from FEMA
indicates that nearly 11,463 homes were severely damaged by Hortense and
agricultural losses were of the order of 127 million dollars. In addition,
there was significant inland flooding in the low-lying areas as well as
serious coastal flooding in Nagabo, Guayanilla and Ponce.
Three people were killed and 21 reported missing in the Dominican
Republic and there was significant damage primarily in the
northeastern portion of the country. A school and one church were
demolished by winds or falling trees, numerous houses were damaged
and several electrical poles went down. There was a 9-foot storm
surge along the northeast coast. Roads were blocked due to flooding
both from the storm surge and from torrential rains. In Samana, 80
percent of the agriculture was damaged.
d. Forecast and Warning Critique
Table 4 summarizes the watches and warnings
associated with Hortense. As indicated in Table 4,
a hurricane watch and a
tropical storm warning
were issued for Puerto Rico when Hortense
was still in the developing stage over the Leeward Islands.
Hortense became sheared and weakened over the eastern Caribbean and
the official intensity forecast called for no significant change in
strength. Consequently, the hurricane watch for Puerto Rico was
discontinued but the tropical storm warning remained in effect.
However, it was emphasized in the tropical cyclone discussions
issued by the NHC that there was low confidence in the intensity
forecast. Hortense reintensified and a
was issued for Puerto Rico about 14 hours before landfall.
Hurricane warnings were in place for the entire island because
hurricanes can often wobble along the track. These wobbles are in
general difficult if not impossible to forecast but are taken into
consideration when issuing watches and warnings. Hortense jogged
to the north of the main track when it was located just south of
Puerto Rico. That wobble or jog brought the center of the hurricane
over the extreme southwestern portion of the island.
Figure 6 (a [82K GIF],
b [87K GIF])
shows a series of model track forecasts for
different periods when Hortense was in the eastern Caribbean. One
can notice that most of the model and official forecasts were to
the left of the best track. This means that, as expected, neither
the models nor the official forecast captured the jog to the north.
However, the errors in the forecast, in general, were much smaller
than the most recent 10-year average forecast errors. Models and
official forecast performance are shown in Table 5.
From the time the tropical cyclone was located over the Lesser
Antilles, NHC advisories as well as
San Juan Forecast Office
statements indicated that 5 to 10 inches of rain, with larger
totals over mountains were expected along the path of Hortense.
Indeed, most of the damage produced by Hortense was caused by rainfall.
Data was primarily provided by
NWS forecast office in San Juan
Puerto Rico, the Dominican Republic Weather Service, and by
Table 4. Watch and warning summary, Hurricane Hortense, September 1996.
||tropical storm warning issued
||Martinique northwestward through the British and U.S. Virgin Islands|
|tropical storm watch issued||Puerto Rico|
|7/2100||hurricane watch and a
tropical storm warning issued
||British and U.S. Virgin Islands and Puerto Rico|
|8/0300||hurricane warning issued
||British and U.S. Virgin Islands|
|8/1500||hurricane warning replaced by
tropical storm warning
||British and U.S. Virgin Islands|
|hurricane watch discontinued||Puerto Rico|
|tropical storm warning discontinued
||From Anguilla southward|
|8/1800||tropical storm warning discontinued
||Northeastern Leeward Islands|
|9/0000||tropical storm watch issued
||Dominican Republic from Cabo Engano to Pedernales of the border of Haiti (south coast)|
|9/1500||hurricane warning issued
|hurricane watch replaces
tropical storm watch
||Dominican Republic from Cabo Engano to the border of Haiti.|
|9/2330||hurricane warning issued
||Dominican Republic from Bahia de Calderas to Peninsula de Samana|
|hurricane watch issued
||Dominican Republic from west of Bahia de Calderas to Pedernales.|
|10/0900||hurricane watch issued
||Turks and Caicos Islands and southeast Bahama
Islands of Mayaguana and Inagua Islands|
|10/1200||hurricane warning extended
||Dominican Republic from Peninsula de Samana to Cabrera.|
|hurricane watch discontinued
||south coast of Dominican Republic|
|10/1500||hurricane warning issued
||Turks and Caicos, Inagua Islands and Mayaguana|
|tropical storm warning discontinued
||U.S. and British Virgin Islands|
|10/1800||hurricane warning discontinued
|10/2100||hurricane warning extended
||north coast of Dominican Republic|
|hurricane watch issued||central Bahamas|
|tropical storm warning and
||north coast of Haiti from St. Nicolas eastward.|
|11/0000||hurricane watch discontinued
||south coast of the Dominican Republic|
|11/1500||hurricane warning discontinued
||hurricane warnings and watches discontinued||Bahamas|