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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 211604

Tropical Weather Discussion 
NWS National Hurricane Center Miami FL 
1605 UTC Wed Sep 20 2017

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 1200 UTC surface analysis and satellite imagery through 
1500 UTC.


A broad area of low pressure along the southwest coast of Mexico 
has a pair of low pressure centers analyzed near 15N97W 1010 mb 
and 17N103W 1008 mb. The area of low pressure is enhancing SW 
monsoon flow between 100W and 115W, producing active convection 
along the Mexico coast north of 16N between 102W and 106W. Model 
guidance indicates this area of low pressure will consolidate 
over the next 24-48 hours, with a tropical depression likely to 
form in about 2-3 days. Environmental conditions are favorable 
for development into a tropical cyclone as the broad low moves 
slowly west-northwest. Extensive heavy rain is expected in parts 
of southern Mexico during the next several days.


A tropical wave along 90W north of 07N is moving west at 10 kt. 
Scattered moderate convection is from 08N to 11N within 150 nm 
east of the wave. The wave is expected to eventually become 
absorbed into the larger monsoon circulation described above.


The monsoon trough stretches across the entire basin from Panama 
near 08N78W to low pres near 17N103W 1008 mb to 14N107W to 
11N127W to 12N140W. Scattered moderate to strong convection is 
from 13N to 19N between 101W and 107W. Scattered moderate 
isolated strong convection is from 10N to 12N between 93W and 
96W. Scattered moderate convection is within 120 nm south of the 
trough axis west of 112W.



A weak surface ridge reaches the central part of Baja California 
near 27N. An approaching cold front moving south across the 
waters west of California is producing fresh to strong SW winds 
in the northern part of the Gulf of California, expected to 
persist through early Fri morning, with seas building to 5-6 ft 
north of 30N. The local effects will be less evident west of 
Baja California and south of 29N in the Gulf of California. 
Elsewhere, the possible development of low pressure along the 
southern coast of Mexico will increase winds and seas between 
100W and 107W the next few days. 


An active monsoon trough along the coast of Central America from 
Guatemala to Panama will help maintain active convection across 
coastal waters the next few days. Expect SW winds south of the 
trough to strengthen gradually to 20-25 knots through Saturday. 
Further south, gentle to moderate southerly winds are expected 
to persist south of 05N through the weekend.


The post-tropical remnant low of Norma is near 23N117W as a 
swirl of low and mid level clouds and stratiform precipitation. 
Winds are estimated to be 20 kt near the center and seas to 7-8 
ft. The low will move slowly and steadily weaken through Friday.

The post-tropical remnant low of Otis is near 16N133W as a swirl 
of low level clouds and limited stratiform precipitation. Fresh 
to strong N-NE winds and 8 ft seas are within 150 nm NW of the 
low center. The low is expected to move SW and weaken into a 
trough through Friday, with seas gradually diminishing to 6-7 ft.

NW swell associated with strong N-NW winds north of the area is 
producing combined seas of 8-10 ft north of 25N between 118W and 
127W, and is expected to contract and shift eastward through 
Friday. Another weaker round of NW swell associated with a cold 
front west of California is expected to arrive Fri night. High 
pressure centered well N of the area and lower pressure 
associated with the convergence zone will maintain moderate 
trade winds west of 120W through the weekend.