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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 220239

Tropical Weather Discussion 
NWS National Hurricane Center Miami FL 
0405 UTC Fri Sep 22 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 0000 UTC surface analysis and satellite imagery through 
0200 UTC.


A broad area of low pressure extends across the southwest coast 
and coastal waters of Mexico persists this evening, where a weak 
surface low pressure center is analyzed near 17.5N104W at 1008 
mb. Just to the south of this, a broad area of fresh to strong 
SW monsoonal winds prevail from 10N to 14N between 99W and 110W, 
producing active convection across this area and creating a very 
unstable atmosphere. Computer model guidance indicates that a 
low pressure center in this general area will shift slowly WNW 
and become better organized over the next 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 across parts of southern Mexico 
and Central America during the next several days.


A tropical wave along about 90W north of 07N this afternoon is 
no longer evident in evening data. Scattered moderate to strong 
convection from 07.5N to 15N between 82W and 93W. The wave has 
become absorbed into the larger monsoonal circulation described 


The monsoon trough stretches across the entire basin from Panama 
near 09N74W TO 09N87W TO low pres near 17.5N104W 1008 MB TO 
13N107W TO low pres near 10N137W 1010 MB TO beyond 11N140W. 
Scattered moderate to strong convection is within 90 nm N and 
120 nm S of the trough between 80W and 90W...and within 90 nm N 
and 180 nm S of the trough between 96W and 140W. 



A weak surface ridge extends ESE across the northern portions 
of the discussion area to the central part of Baja California 
near 26N. An approaching cold front moving south into the far 
northern waters extends from 30N119W to 29N124W to 30N133W. The 
pressure gradient between high pressure behind the front and 
troughing across northern Mexico 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 5-7 
ft north of 29N. As the high pressure behind the dissipating 
front builds SE into the area during the next couple of days, 
NWly winds will freshen slightly west of Baja California Norte, 
while little effects will be seen 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 22N116.5W 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 7-9 
ft. The low will move slowly SE and steadily weaken through 

The post-tropical remnant low of Otis is near 14.5N133.5W as a 
swirl of low level clouds and limited stratiform precipitation. 
Fresh 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 20N between 117W and 
135W, 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 monsoon trough will maintain moderate trade 
winds west of 120W through the weekend.