The southern extension of the tropical wave that triggered Tropical Storm
Emily in the Atlantic moved westward through the Caribbean Sea for several
days and crossed Central America between 31 August and 1 September
(Fig. 1). Satellite imagery revealed a middle-level
circulation with a large area of thunderstorms associated with the wave
moving westward partially inland over southern Mexico. A large area of
disturbed weather associated with a cyclonic monsoon-type flow had prevailed
over the eastern Pacific for several days. However, it was not until the
tropical wave arrived in the area that tropical cyclone formation began.
The thunderstorm activity became concentrated while cloud banding features
were developing. Dvorak T-numbers suggested the formation of a 30-knot
tropical depression very near Manzanillo, Mexico at 1200 UTC 5 September.
It appears that the same tropical wave combined with the strong southwest
monsoonal-type flow which extended northward into the Bay of Campeche, led
the formation of the Atlantic Tropical Depression Seven in the Gulf of
Mexico during that period.
The eastern Pacific depression continued to become better organized, and
both satellite images and ship reports indicated that the tropical cyclone
reached tropical storm strength by 1800 UTC on the same day. Greg was then
moving on a general northwest track very close to the southwestern coast of
Mexico. A large area of very deep convection formed near the center of
circulation and radar from Los Cabos, Mexico suggested the formation of an
ragged eye during the morning of 6 September. Greg was upgraded to
hurricane status at 1800 UTC on the same day while approaching the southern
portion of Baja California. Figure 2 display the radar
presentation of Greg and a visible satellite image of the hurricane near the
time of its peak intensity. No significant change in strength occurred for
the next 24 hours, and thereafter, Greg weakened to tropical storm status as
its center moved over the area of Cabo San Lucas around 2100 UTC 7
September. Greg turned toward the west-northwest and west over cooler
waters and weakening began. Greg's track is shown in
Fig. 3. Table 1 is a
listing, at six-hourly intervals, of the best-track 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. 4 and are primarily based on satellite intensity
estimates from the Tropical Analysis and Forecast Branch (TAFB), the
Satellite Analysis Branch (SAB) and the Air Force Weather Agency, (AFGWC in
figures). Operationally, Greg was upgraded to tropical storm based on data
from the ship 3EJO6, which reported winds of 230 degrees with 42 knots and a
pressure of 1006.5 mb at 1800 UTC 5 September. Greg produced torrential
rains over portions of southwestern Mexico. Nearly 9 inches were measured
in Manzanillo, about 8 inches in Colima and 5 inches in Islas Marias as Greg
moved nearby. San Jose del Cabo, on the southern tip of Baja California,
reported sustained winds of 35 knots with gusts to 40 knots and a minimum
pressure of 995 mb at 2100 UTC 7 September while the center of Greg was
crossing the southwestern tip of Baja California.
c. Casualty and Damage Statistics
Reports from the El Nuevo Herald indicate that torrential rains caused
extensive flooding over the states of Colima, Jalisco, Michoacan, Nayarit
and Sinaloa. Nine people were killed as a consequence of the rains.
d. Forecast and Warning Critique
Because Greg formed very close to the southwest coast of Mexico, tropical
storm warnings were required immediately and were issued in the first
advisory. Additional watches and warnings were issued for portions of Baja
California. A summary is included in Table 2. Both
official forecasts and the Statistical Hurricane Intensity Prediction Scheme
(SHIPS) indicated that Greg would peak at 65 knots.
The NHC average official track errors (in n mi) for Greg (excluding the
tropical depression stage) were 35 (10 cases), 59 (8 cases), 98 (6 cases),
132 (4 cases), respectively, for the 12-, 24-, 36-, 48-hour forecast
periods. There were no 72-hour forecast to verify. These errors for 12,
24, 36 and 48 hour periods are very near the 1989-1998 average official
Sequence of daily GOES 8 satellite images at 1200 UTC from 27 August to 4
September 1999. Dashed line marks the westward propagation of the tropical
wave which eventually triggered Hurricane Greg (G).
View of Hurricane Greg at 1917 UTC September 6 from San Jose del Cabo radar.
Visible satellite image of Hurricane Greg at 0000 UTC 7 September, near the
time of peak intensity.
Best track positions for Hurricane Greg, 5-9 September 1999.
Best track minimum central pressure and maximum speed curves for Hurricane
Best track, Hurricane Greg, 5-9 September, 1999
|7/2100||22.9||110.0||994||50||landfall near Cabo San Lucas
Tropical Cyclone watch and warning summary for Hurricane Greg.
|5/1600||Tropical Storm Warning||for the coast of Mexico from Manzanillo to Cabo Corrientes including Islas Marias.
|5/2100||Tropical Storm Warning extended southeastward||to include Lazaro Cardenas.
|6/0300||Tropical Storm Warning issued||for the east coast of Baja California south of La Paz.
|6/0300||Tropical Storm Watch issued||for the west coast of Baja California south of Punta Abreojos.
|6/0900||Tropical Storm Warning issued ||for the west coast of Baja California south of Cabo San Lazaro.
|6/1500||Hurricane Warning||for the west coast of Baja California from arroyo Seco southward and for the east coast from La Paz southward.
|6/2100||Tropical Storm Watch||for the east coast of Baja California fron north of La Paz to Loreto.
|7/2100||change hurricane warning to tropical storm warning||for Baja California from Arroyo Seco southward and from La Paz southward.
|8/0900||Tropical Storm Warning and Watch discontinued||for the east coast of Baja California
|8/1500||Tropical Storm Warning and Watch discontinued||all areas.