000 AXPZ20 KNHC 090325 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 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 0000 UTC surface analysis and satellite imagery through 0300 UTC. ...SPECIAL FEATURE... Gulf of Tehuantepec Gale Warning: Strong high pressure is blasting S 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 beginning around dawn Sun. These N winds will quickly increase to strong gale force beginning Sun afternoon. Seas in the gale area are forecast to build to between 11 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. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from northern Colombia near 08N76W across Panama to 08N90W. The ITCZ continues from 08N90W to 07N95W to 09N101W, then resumes from 09N105W to 07N117W to beyond 08N140W. Numerous moderate and isolated strong convection is taking place from 07N to 10N W of 138W. Scattered moderate and isolated strong convection is found elsewhere from 06N to 11N W of 133W. A surface trough splits the ITCZ from 07N103W to 12N102W. Numerous moderate and isolated strong convection is occurring from 11.5N to 12.5N between 102W and 105W. Scattered moderate and isolated strong convection is present elsewhere within 90 nm either side of a line from 07.5N100.5W to 12.5N103.5W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Recent satellite-derived wind data confirmed long period northwest swell are maintaining seas of 7 to 9 ft spread across much of the offshore waters of Baja California. Seas are expected to subside a couple of feet by Sun night as the NW swell decay. Another round of NW swell will reach the northern coastal waters of Baja California Norte by Mon evening, as well as Guadalupe Island. Seas exceeding 8 ft will encompass most the offshore waters of Baja California and the Revillagigedo Islands through Tue evening, before subsiding below 8 ft through mid week. High pressure of 1026 mb is centered near 32N124W. This high will merge with a larger high moving in from the west by Mon afternoon. The pressure gradient between this area of high pressure and lower pressure in the vicinity of the Baja Peninsula will primarily maintain moderate to occasionally fresh north to northeast winds over the offshore waters through Mon night. Winds begin to increase late Mon night into early Tue over the northeast part of the area as merged high pressure builds east- southeast across these waters. The combination of strong high pressure building over the Great Basin and troughing along and near the Gulf of California is expected to produce a narrow swath of fresh to locally strong NW to N winds across the Gulf of California within about 60 nm of the E coast of Baja California Sur Sun afternoon to late Sun night. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo...Winds and seas have diminished for the time being. However, Winds will once again pulse during the overnight and early morning hours over the Gulf of Papagayo Sun night through Wed night as high pressure shifting E over the Gulf of Mexico builds S toward the NW Caribbean Sea and Central America. An area of moderate to fresh E winds well W and SW of the Gulf has seas in the 6 to 8 ft range from mixed swell. 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 32N137W to 28N140W. Long-period NW swell will continue propagating SE to encompass almost all of the forecast waters west of 105W tonight, ahead of a reinforcing batch of swell approaching from the NW associated with the second front. Much of the older swell will decay north of 20N through early Sun. Combined seas from trade winds and swell will support a large area of 8 to 10 ft seas south of 20N by Sun night, eventually mixing with the longer period NW reinforcing swell moving across the basin west of 120W through Tue. Farther east, a surface trough persists from 07N103W to 12N102W. Scatterometer data from early this evening indicated winds to 25 kt on the northern portion of the trough. Satellite imagery shows showers and thunderstorms continuing in the vicinity of the trough within 90 nm either side of a line from 07.5N100.5W to 12.5N103.5W. The trough is forecast to continue to move westward and weaken through Sun night. Meanwhile, a large area of 8 ft seas associated with mixed swell will develop Wed morning from 03N to 13N between 90W and 110W, mainly comprised of long period NW swell and shorter period northeast swell propagating downstream from the Gulfs of Tehuantepec and Papagayo. $$ CAM