000 AXPZ20 KNHC 082201 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2013 UTC Sat Dec 8 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. ...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 pres S of Mexico will result in an abrupt onset of strong to near gale force N winds, which will surge S 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 diminish further and become light by Wed evening as the strong high over eastern Mexico 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. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from northern Colombia near 08N77W across Panama to 08N90W. The ITCZ continues from 08N90W to 07N94W to 08N98W, then resumes from 08N104W to 07N124W to beyond 09N140W. Numerous moderate and isolated strong convection is occurring from 07N to 10N W of 133W. within 90 nm of the ITCZ west of 130W. A surface trough splits the ITCZ from 07N101W to 11N100W. Scattered moderate and isolated strong convection is found from 08N to 12N between 99W and 102W. An area of convergent trade winds is generating scattered moderate and isolated strong convection well to the S of Cabo San Lucas from 11N to 16N between 108W and 113W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Recent satellite-derived wind data confirm seas of 8 to 10 ft spread across much of the offshore waters of Baja California. This is due to persistent long period NW swell. Seas are expected to subside below 8 ft through early Sun as the NW swell decay. Another round of NW swell will reach the northern coastal waters of Baja California Norte by late Mon, as well as Guadalupe Island. Swell in excess of 8 ft will envelop most the offshore waters of Baja California and the Revillagigedo Islands through late Tue, before subsiding below 8 ft through mid week. The pressure gradient between a 1027 mb high analyzed near 32N124W that is moving NE and comparatively lower pressure in the vicinity of the Baja Peninsula will primarily maintain moderate to occasionally fresh N to NE winds over the offshore waters through Mon night. Winds begin to increase late Mon night into early Tue over the NE part of the area as strong high pressure builds ESE 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 dissipating cold front extends from 30N148W to 29N140W. This front lies ahead of a stronger reinforcing front approaching the area from the west. Long period NW swell will continue propagating SE to encompass almost all of the forecast waters west of 105W tonight, ahead of a reinforcing group 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 07N101W to 11N100W. Earlier scatterometer data indicated winds to 25 kt on the northern portion of the trough. Satellite imagery shows scattered showers and isolated thunderstorms persisting within 90 nm of the trough from 08N to 12N. The trough is forecast to continue W through Sun night and weaken. Meanwhile a large area of 8 ft seas associated with mixed swell will develop from 03N to 13N east of 110W, mainly comprised of long period NW swell and shorter period NE swell propagating downstream of the Gulf of Tehuantepec. $$ CAM