Some tropical cyclones in the
eastern North Pacific appear to develop
in close association with tropical waves.
Others, like Hurricane Flossie, are apparently generated in a different,
"monsoon-like" mode of formation in which tropical waves may not
be the primary large-scale forcing.
a. Synoptic History
Hurricane Flossie formed within a large, deep cyclonic
circulation and low pressure area that dominated the weather in the
tropical eastern North Pacific Ocean near the end of the first week
of August. The southern and southeastern part of this area was
defined by a long stretch of west-southwesterly winds and by
cloudiness in the eastern part of the ITCZ, which had pivoted
northward through the Gulf of Tehuantepec (toward
Tropical Storm Gabrielle
in the western Gulf of Mexico).
The large circulation was well-developed by August 7 when
thunderstorm activity began to increase and become focussed a few
hundred miles southwest of Acapulco (perhaps in association with a
tropical wave analyzed in the vicinity). Surface pressures were
already low across the region as implied by a ship report of 1004.0
mb made near Acapulco at 0000 UTC on the 7th. Based primarily on
surface analyses, this system is estimated to have become
Tropical Depression Seven-E at
1200 UTC on the 7th (Table 1
and Fig. 1 [42K GIF]).
The intensity implied by satellite images continued to lag the
estimates derived from surface reports. Satellite analysts at the
NHC and NESDIS
Synoptic Analysis Branch
(SAB) had Dvorak
T-numbers of 2.0 (30 knots) at 0000 UTC on the 9th
(Figs. 2 [24K GIF]
and 3 [25K GIF]).
However, two ships then had pressures in the 996-999 mb range and
observations from ships imply that winds were likely of
tropical storm force.
It is now estimated that the depression became
Tropical Storm Flossie at 1800 UTC on the 8th.
Flossie moved toward the northwest at 5 to 10 knots for most of its
seven-day existence, to the south-southeast of a deep-layer-mean anticyclone.
On this course, the center
remained offshore, but the southwestern coast of Mexico and later the southern Baja
California peninsula were buffeted by gusty winds and locally heavy
A northeasterly vertical wind shear diminished and very cold
cloud tops then developed. Flossie reached hurricane
strength on the 10th and its peak intensity, 70 knots, was maintained for about
24 hours beginning at 1200 UTC that day. An embedded warm spot
appeared in satellite pictures and the center of circulation made
its closest approach to land during that period, when it passed
about 65 n mi to the southwest of the peninsula.
Weakening ensued over cooler waters. Flossie dropped below
hurricane strength on the 12th and turned westward. It was a
depression on the 13th and dissipated on the 14th.
b. Meteorological Statistics
Figures 2 and 3
show the curves of estimated minimum central pressure and maximum one-minute wind speed versus time,
respectively, and the data upon which they were based. The
Air Force Global Weather Central (AFGWC),
the NHC Tropical Analysis and Forecast Branch (TAFB; TSAF in figures), and the
NESDIS Synoptic Analysis Branch (SAB)
supplied the Dvorak classifications. The figures show the early lag between Dvorak technique
intensity estimates derived from satellite pictures and estimates made from
An observation of tropical storm force winds was received from
Cabo San Lucas, Baja California which had 35 knot winds (over 10-minutes)
and a gust to 48 knots at 0300 UTC on the 11th. Nearby
San Jose del Cabo had a gust to 55 knots according to amateur radio
reports. Selected significant ship observations are as follows:
|Lat. (°N)||Lon. (°W)
Some data from the ship LAMF2 are likely unrepresentative.
c. Casualty and Damage Statistics
The El Nuevo Herald newspaper reported five lives lost in
Puerto Vallarta and Mazatlan. Amateur radio reports stated that
two people drowned in Cabo San Lucas. No quantitative estimates of
damage have been received.
d. Forecast and Warning Critique
Flossie was of tropical storm or hurricane intensity for only
about four days so there were few forecasts to evaluate. On
average, the NHC track and intensity errors for that period were
comparable to previous averages.
Table 2 lists tropical storm warnings and watches issued by
the Government of Mexico.