AXPZ20 KNHC 220944

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
655 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 0600 UTC surface analysis and satellite imagery through 0830 UTC.


A broad and elongated area of monsoonal low pressure persists along the southwest coast and coastal waters of Mexico this morning. A weak 1007 mb surface low pressure center is analyzed within this broad area of low pressure near 16.5N104.5W. An area of associated fresh to strong SW monsoonal winds is evident from 08N to 12N between 110W and 116W. Convergent monsoonal winds continue to produce vigorous convection along the coast of mexico between Cabo Corrientes and Chiapas and also along the coast of Guatemala. Computer model guidance continues to show that the low will shift slowly NW and gradually become better organized during the next several days. The area of vigorous convection will continue to plague parts of southern Mexico and Central America with heavy rains during the next several days.


The monsoon trough stretches across the entire basin from NW Colombia near 09N73W TO 08N79W to 13N90W to low pres 1007 mb near 16.5N104.5W to 14N115W to 12N119W to low pres 1012 mb near 11N137W to beyond 12N140W. Scattered moderate and isolated strong convection is seen within 60 nm NE and 210 nm SW of the trough axis between 87W and 96W, from 16N to 20N between 105W and 108W and from 07N to 11N between 135W and 140W. Scattered moderate convection is present along and up to 210 nm S of the trough axis between 97W and 133W.



A surface ridge extends SE across the northern portions of the discussion area to the central part of Baja California near 26N. An cold front pushing south into northern waters curves west from 31N116W to 27.5N125W to 30N138W. The cold front is producing fresh to strong SW winds in the northern part of the Gulf of California. These winds are expected to linger a while longer this morning until the front departs to the east, with associated seas of 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, NW winds will freshen slightly west of Baja California Norte, while little influence from the high 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 101W and 117W the next few days.


An active monsoon trough following the coast of Central America from Guatemala to Panama will remain a focus for active convection over the coastal waters during the next few days. Expect SW winds south of the trough to strengthen gradually to 20-25 knots through Saturday. Farther south, gentle to moderate south to southwest winds are expected to persist south of 05N through the weekend. Long period SE swell from the Southern Hemisphere will maintain seas west of Ecuador and south of 02S around 8 ft today before the swell decay and seas subside below 8 ft.


The post-tropical remnant low of Norma is centered near 22N116W as a swirl of low to mid level clouds. Winds are estimated to be 20 kt near the center. Seas of 8 to 9 ft are confined to the west quadrant within 270 nm of the center of the low. The low will drift slowly SE and weaken into a trough by Saturday morning.

NW swell generated by strong N to NW winds north of the area are producing combined seas to 8 ft north of 25N between 117W and 127W. This area of combined seas is expected to subside below 8 ft by this evening. Another weaker round of NW swell associated with a cold front west of California is expected to arrive tonight. High pressure centered well N of the area and lower pressure associated with the monsoon trough will maintain moderate to occasionally fresh trade winds west of 120W through the weekend.

$$ CAM