000 AXPZ20 KNHC 091536 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1536 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 1200 UTC surface analysis and satellite imagery through 1500 UTC. ...SPECIAL FEATURE... 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. The onset of these winds has recently begun to affect the northern tier of the Gulf. These north winds will quickly increase to strong gale force beginning this afternoon. Seas in the gale area are forecast to build to between 10 and 17 ft by late Sun night. 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 south and southwest 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. Fuego Ashfall Advisory: The Fuego Volcano in Guatemala is in a state of unrest. Easterly winds are carrying a significant and persistent plume of ash up to 120 nm into the Pacific waters off the coast between San Jose Guatemala and Tapachula Mexico. The plume of ash is expected to reach as far as 180 nm off the coast through 24 hours. Coastal observations indicate the ash is likely elevated and not impacting surface visibility at this time. However, as this event persists over the water through at least the next 24 hours, mariners transiting along this coastline should use caution due the potential for limited visibility and possibly ash accumulations over the water. If mariners encounter ash or floating volcanic debris, you are encouraged to report the observation to the National Weather Service by calling 1-305-229-4425. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from northern Colombia near 07N78W to 05N83W to 06N90W, where latest scatterometer data indicates that ITCZ begins and continues to 07N100W where it briefly ends to the east of a surface trough that extends from 14N107W to 07N107W. The ITCZ resumes from 09N110W to 10N120W to to beyond 07N140W. Scattered moderate convection is noted on the northern end of the surface trough from 11N to 15N between 106W and 110W. Scattered moderate to isolated strong convection noted from 05N to 07N between 114W and 118W. Scattered moderate convection within 60 nm south of ITCZ between 125W and 129W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A 1026 mb high pressure area is centered west of northern Baja California Norte near 32N123W. 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 altimeter satellite passes confirm most of the large, long-period NW swell inundating the open waters over the past couple of days has 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. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... 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. REMAINDER OF THE AREA... 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. Earlier scatterometer data indicated a surface trough from 14N107W to 07N107W. The scatterometer revealed east to southeast winds within about 60 nm either side of the trough from 10N to 12N. Seas with these winds are in the range of 6 to 8 ft. Satellite imagery shows scattered showers and thunderstorms from 11N to 15N between 106W and 110W. The trough is forecast to continue to move westward and weaken through tonight. 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. $$ Christensen