AXPZ20 KNHC 230935

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
626 UTC Sat Sep 23 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 0600 UTC surface analysis and satellite imagery through 0830 UTC.


A broad elongated area of low pressure remains in place along the southwestern coast of Mexico and adjacent coastal waters, from Manzanillo to just south of the Gulf of Tehuantepec. The latest satellite-derived wind data indicated this area of low pressure remains weak and winds in the vicinity of the circulation are 20 kt or less. However, the latest IR satellite imagery shows deep convection has flared during the past several hours on the west side of the circulation, which is centered near 17.5N104.5W, with an estimated pressure of 1007 mb. To the S of the low and detached from it is a large belt of fresh to locally strong SW monsoon winds, roughly from 10N to 14N between 100W and 120W. Model guidance indicates that the low retains the potential to develop into a tropical cyclone as it slowly drifts NW. toward the southern Gulf of California. The convergent monsoonal winds will continue to generate widespread active convection along and near the coast of Mexico and Central America, with heavy rains likely to persist in this area at least several more days.


The monsoon trough stretches across the entire basin and extends from northern Colombia near 10N74W to just north of Panama near 11N77W to Costa Rica near 09N84W to the Gulf of Tehuantepec near 16N95W to low pres 1007 mb near 18N105W to 12N126W to low pres 1011 mb near 14N137W to beyond 11N140W. Scattered moderate and isolated strong convection is found along and up to 180 nm SW of the trough axis between 90W and 96W and from 10N to 12N between 129W and 134W. Scattered moderate convection is present within 90 nm either side of a line from 13N98W to 11N120W.



A weakening cold front extends from SE Arizona SW across the central Gulf of California and northern Baja California Sur, then WSW to beyond 24N117W. Latest satellite-derived wind data showed moderate to fresh NNW winds behind the front over the offshore waters. Expect the front to push farther south and dissipate by this evening. High pressure will build north of 25N behind the front through Sun, with NW winds increasing slightly west of Baja California Norte. Elsewhere, the expected development of low pressure along the coast of Mexico south of Cabo Corrientes will increase winds and seas from Cabo Corrientes to the southern Gulf of California during the next few days.


An active monsoon trough undulating along the coast of Central America from Guatemala to Panama will remain the focus for active convection over the coastal waters the next few days. Expect SW winds south of the trough to increase from moderate to fresh speeds during the next few days. Farther south, gentle to moderate south to southwest winds will persist south of 05N through the weekend. Long period SE swell from the Southern Hemisphere will remain high enough to maintain seas west of Ecuador and south of the Equator around 7-8 ft through this evening.


NW swell generated by strong N to NW winds north of the area are producing combined seas to 8 ft north of 28N between 116W and 123W. This area of combined seas will subside around 1 foot during the next 24 hours. High pressure centered well N of the area and lower pressure associated with the monsoon trough will combine to maintain moderate to occasionally fresh trade winds west of 120W through Mon. Low pressure passing north of the area will weaken the high and cause the trades to decrease during the second half of next week.

$$ CAM