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 above.


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 Friday.

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.

$$ Stripling