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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 160926

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
701 UTC Tue Oct 16 2018

Tropical Weather Discussion for the eastern Pacific Ocean from
the Equator to 32N, east of 140W. The following information is
based on satellite imagery, weather observations, radar, and
meteorological analysis.

Based on 0600 UTC surface analysis and satellite imagery through
0845 UTC.


The center of Tropical Storm Tara is located near 18.7N 104.5W 
at 16/0900 UTC or 20 nm SSW of Manzanillo Mexico drifting NNW or 
335 degrees at 2 kt. Estimated minimum central pressure is 998 
mb. Maximum sustained wind speed is 50 kt with gusts to 60 kt. 
Numerous moderate and scattered strong convection is noted within
60 nm in the NW and within 30 nm in the SE semicircle. Scattered
moderate and isolated strong convection is seen elsewhere from 
17.5N to 20N between 103.5W and 106W. The system is forecast to 
move slowly toward the northwest during the next day or so. On 
the forecast track, the center of Tara should pass very close to 
the coast of southwestern Mexico, or possibly move inland, today 
or Wednesday. Gradual weakening is forecast as Tara interacts 
with the mountains of southwestern Mexico. See latest NHC 
forecast/advisory under AWIPS/WMO headers MIATCPEP2/WTPZ32 KNHC 
for more details.

Gulf of California: Frequent gusts to gale force over the 
northern Gulf of California have ended as winds begin to subside.
A recent ASCAT pass from around 04Z provided observations of 20 
to 25 kt sustained winds over Gulf of California N of 27N. These 
winds are caused by high pressure over the Great Basin of the 
United States. The fresh to strong winds are expected to subside 
by Wed morning as the high moves E and weakens.


The monsoon trough extends from 17N85W to a 1007 mb low pressure
centered over the far SW Caribbean near 16N87W, then across 
Central America to near the Gulf of Tehuantepec at 17N95W to 
12N106W to 12N116W to 09N121W to 10N130W to beyond 08N140W. 
Numerous moderate and scattered strong convection is found from 
04N to 07N E of 78W. Scattered moderate and isolated strong 
convection is seen N of a line from 07N82W to 11N92W and within 
180 nm of the monsoon trough axis W of 95W. 



Latest scatterometer data indicate moderate to locally fresh NW 
winds over the offshore forecast waters W of Baja California. A 
ridge currently extending from 1022 mb high pressure centered 
near 35N127W to near the Revillagigedo Islands will maintain its 
influence over the offshore waters W of Baja California 
Peninsula. Gentle to moderate NW to N winds, and seas generally 
in the 4 to 6 ft range will prevail through Thu night. Seas are 
forecast to remain largely unaffected by Tropical Storm Tara.

Gulf of Tehuantepec: Next gap wind event is forecast to start 
early on Wed with seas rapidly building to 10 ft by Wed 
afternoon. This event will be associated with a ridge building 
behind a cold front sliding S along the eastern slopes of the 
Sierra Madre Mountains in Mexico and the western Gulf of Mexico.


Moderate to fresh SW monsoonal flow will continue across the 
region through Tue, with showers and thunderstorms expected to 
continue along the Pacific coast of Central America. Long period 
cross-equatorial SW swell will maintain 5 to 8 ft seas across the
forecast area during this time frame. By Tue night and Wed, 
marine guidance suggests an increase in winds and seas across the
offshore waters from northern Costa Rica to Guatemala. This 
appears to be associated with an area of low pressure forecast to
develop a couple of hundred miles south of Guatemala and the 
southeastern coast of Mexico around mid-week. This system retains
a high chance of becoming a tropical depression during the next 
5 days as it tracks WNW along the southern coast of Mexico.


The pressure gradient between the high pressure ridge to the W 
of the Baja Peninsula and a cold front approaching from the W is 
generating fresh to strong southerly winds across the far NW 
waters, mainly NW of a line from 30N138W to 26N140W. Moderate to 
locally fresh trades are noted S of 15N and N of the monsoon 
trough W of 125W. The cold front is forecast to reach a position 
from 30N138W to 27N140W on Tue, and then from 30N138W to 27N138W 
to 25N140W as a weakening stationary front on Wed. Long period NW
swell will follow the front and cause seas to build to between 8
and 10 ft generally N of 15N and W of 132W.

Satellite-derived wind and altimeter data confirmed the presence
of moderate to fresh monsoonal flow over the forecast waters N of
07N and S of the monsoon trough. Winds increase near the 
convection. An area of 7 to 9 ft in long period SW swell is noted
south of the monsoon trough and mainly between 100W and 115W.

Looking ahead, an area of low pressure is forecast to develop a 
couple of hundred miles south of Guatemala and the southeastern 
coast of Mexico by late Wed. Environmental conditions are 
forecast to be conducive for development, and a tropical 
depression is likely to form by late week while the system moves 
west- northwestward near the southern coast of Mexico. The latest
Tropical Weather Outlook gives this system a high change of 
tropical cyclone formation through 5 days.