AXPZ20 KNHC 092205

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2151 UTC Sun Dec 9 2018

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 1800 UTC surface analysis and satellite imagery through 2045 UTC.


Gulf of Tehuantepec Gale Warning: High pressure is pressing southward along the eastern slopes of the Sierra Madre Oriental mountains of Mexico. The large pressure difference between the high and lower pressure south of Mexico will result in an abrupt onset of strong to near gale force north to northeast winds, which will surge southward across the Isthmus of Tehuantepec and out over the Gulf of Tehuantepec. Strong winds have already begun to affect the Gulf N of 14N. These winds will quickly increase to strong gale force this evening. Seas in the gale area are forecast to build to between 12 and 18 ft by late tonight. The strong gale force winds will continue through Tue, then diminish to minimal gale force Tue night. Winds will then quickly decrease and become light by Wed evening as the strong high over the Gulf weakens and shifts eastward. Swell from this event is forecast to propagate S and SW well away from the Gulf of Tehuantepec region, with the leading edge of the 8 ft seas expected to reach near 09N110W by late Tue night or Wed. Please refer to the Eastern Pacific High Seas Forecast under AWIPS/WMO headers HSFEP2/FZPN03 KNHC for more specific marine details.


The monsoon trough axis extends from low pres 1010 mb near 06N74W to 05N83W to 05N90W. The ITCZ continues from 05N90W to 07N104W, then resumes from 10N113W to 09N123W to beyond 07N140W. Scattered moderate and isolated strong convection is noted within 90 nm either side of a line from 05N118W to 08N131W. A surface trough splits the ITCZ from 06N109W to 10N109W to 14N109W. Scattered moderate and isolated strong convection is seen from 11N to 14N between 105W and 110W.



A 1027 mb high pressure area is centered west of northern Baja California Norte near 32N124W. Strong high pressure is currently centered over the Great Basin as well. The pressure gradient between these high pressure areas and enhanced troughing across the Gulf of California is supporting fresh to strong NW winds across mainly southern half of the Gulf of California. Seas in this area are estimated to be as high as 5 ft. Looking ahead, strong high pressure building over the Great Basin well north of the area will support strong NW winds over mainly the northern Gulf of California Thu.

Recent satellite-derived sea height data show most of the large, long- period NW swell inundating the open waters over the past couple of days have subsided below 8 ft, with the exception of the area near the Revillagigedo Islands. A new group of NW swell in excess of 8 ft will reach the waters off the northern Baja California coast and near Guadalupe Island by late Mon, then spread east to cover most of the waters off the entire Baja California peninsula and the Revillagigedo Islands through Tue night, before subsiding below 8 ft through Wed.


Gulf of Papagayo...Winds will pulse to strong intensity during the overnight and early morning hours over the Gulf of Papagayo beginning tonight and through Wed night as high pressure shifting eastward over the Gulf of Mexico builds southward toward the NW Caribbean Sea and Central America.

Elsewhere, gentle to moderate winds will persist on either side of a weakening monsoon trough and seas in the range of 4 to 6 ft.


A cold front extends from near 32N133W to 27N140W. Long-period NW swell is following in behind this front, and will bring seas in excess of 8 ft over most of the area west of 120W through early Tue. This will reinforce older, decaying NW swell lingering south of 20N, mixed with shorter period trade wind swell. High pressure building behind the front will support generally fresh trade winds over the deep tropics west of 125W through mid week, with fresh to strong winds possible west of 135W. Trade wind convergence along with an assist from divergent flow aloft on the southeast side of a broad upper trough over Hawaii is supporting clusters of showers and thunderstorms along the ITCZ, and this will persist sporadically through early in the week.

Wave model guidance suggests that a rather large area of 8 ft seas associated with mixed swell will exist Wed morning from about 03N to 13N between 94W and 110W as a result of long period northwest swell mixing with shorter period northeast swell that propagate downstream from the Gulf of Tehuantepec and to a smaller extent those induced by the Gulf of Papagayo strong pulsing northeast winds.

$$ CAM