Tropical Storm Andres moved toward the east to southeast,
near the coast of Central America, for several days. This evolution
was unprecedented in the NHC data base comprising more than 700
eastern North Pacific tropical cyclone
tracks during the period 1949-1997.
a. Synoptic History
The upper-level westerlies extended to rather low latitudes over
the eastern North Pacific Ocean through most of the month of May.
The associated westerly vertical wind shear helped inhibit
tropical cyclone formation in that basin during May.
Near the end of the month, however, the westerlies lifted northward slightly over the
easternmost part of the basin. It was there that a distinct
circulation of low- to mid-level clouds developed on 30 May,
possibly in association with a tropical wave that crossed the
Atlantic Ocean at low latitudes from 14-28 May. On the 31st, deep
convection developed and became concentrated near the
center of the cloud pattern.
Satellite intensity estimates from the Dvorak
technique reached T1.5-2.0 early on 1 June and are the bases for
estimating that the disturbance became a tropical depression
at 0000 UTC on 1 June, about 300 n mi south of the Gulf of Tehuantepec
(Figs. 1 (23K GIF), 2 (22K GIF),
and 3 (25K GIF), Table 1).
Satellite analyses imply that as the cloud pattern became elongated
generally from north to south on 2-3 June, a second cloud center to
the north-northwest of the original center became dominant. The
cyclone strengthened slightly early in this period and became
Tropical Storm Andres.
Andres initially moved toward the northwest. This track gradually
brought the tropical storm into a pattern of westerly steering
winds and, by midday of the 3rd, the storm was moving toward the
east to east-northeast. This heading was toward the mainland and
the first in a series of tropical storm warnings
for southeastern Mexico and Central America was issued (Table 2). Andres moved to
within about 30 n mi of the coast of Guatemala and strengthened a
little, to its maximum intensity of 45 knots.
The axis of a short-wave trough passed a little to the north, over
the Bay of Campeche, on the 4th. The northwesterly flow behind the
axis steered Andres toward the southeast on a course roughly
parallel to the coast. On this track, Andres' cloud pattern became
rather shapeless while the cyclone interacted increasingly with
ITCZ clouds and a monsoon-like circulation associated with the
ITCZ. The storm then weakened.
Late on 6 June, Andres began moving northward at the head of a band
of convective cloudiness that extended southwestward to the ITCZ.
Andres made landfall on the coast of El Salvador near 0000 UTC on
the 7th as a tropical depression. It was the first landfall in
that country (records begin 1949).
The surface circulation became disrupted by the high terrain of
Central America and is estimated to have dissipated a few hours
after landfall. A mid-level cloud remnant continued to circulate
and move northward over land. When that feature reached the Gulf
of Honduras, a weak surface low redeveloped. Eventually, the
rejuvenated system contributed to heavy rain over western Cuba, the
southern Florida peninsula and the northwestern Bahamas. The low
gradually combined with a weak, non-tropical trough over the
eastern Gulf of Mexico. The last "fix" on the low
was over the eastern Gulf of Mexico on 10 June.
b. Meteorological Statistics
Figures 2 and 3
show the tropical storm's estimated central pressure and maximum one-minute wind speed,
respectively, versus time and the associated satellite data. Position and intensity
estimates from satellite pictures were provided by the
Air Force Global Weather Center
(AFGWC), NOAA Tropical Analysis and Forecast Branch (TAFB) and NOAA
Synoptic Analysis Branch (SAB).
The NHC has not received official reports of surface observations
of tropical storm force winds associated with Andres. The analysis
of Andres' surface wind field was improved by near real-time wind
speed and direction data received from a NASA scatterometer
(NSCAT). This was the first operational use of this data by the
NHC.
According to El Nuevo Herald, Andres generated torrential
showers and locally enormous seas and inundations along the western Central
America coast.
c. Casualty and Damage Statistics
A reprinting of Nicaragua's La Prensa by El Nuevo Herald
indicated that two fisherman were missing. There were no other reports of
casualties.
El Nuevo Herald attributed to Andres interruptions to electricity,
overflowing rivers, automobile accidents and damage to about 10
homes in El Salvador and Nicaragua. Damage was noted in the
Nicaragua municipalities of Chinandega, Corinto, El Realejo and El Viejo.
d. Forecast and Warning Critique
Some of the track model guidance normally used by the forecasters
was not available for a variety of technical reasons (see
Table 2).
When Andres approached the coast of Guatemala most of the
available model forecasts and the NHC forecast track incorrectly showed a
continued east to northeast movement, implying Andres would then
cross Central America and emerge into the western Caribbean Sea.
Several of the models showed a threat to Cuba, the Gulf of Mexico,
and Florida, within the following two to three days. Some also
showed cyclongenesis of a major storm over the eastern Gulf of
Mexico. Neither occurred. With the exception of BAMS, track
forecast errors were considerably larger than normal.
The NHC intensity forecasts were mostly 5 to 15 knots too low,
primarily due to the incorrect expectation that Andres would move
inland and weaken (a few days before that actually occurred).
Table 3 lists the watches and
warnings issued in association with Andres. The initial tropical storm warning was
not preceded by a tropical storm watch. The
possibility that either a watch or warning might soon be issued was, however, noted
in each advisory during the 27 hours leading up to the warning.
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