000 AXPZ20 KNHC 162229 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Sun Dec 16 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 2030 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: The tight pressure gradient over southeastern Mexico resulting from the combination of strong high pressure over northern Mexico and lower pressure south of Mexico continues to produce strong gale force northerly winds over the Gulf of Tehuantepec and downstream to near 14N95.5W, where seas area around 16 ft. This gale force gap wind event will continue through tonight, before diminishing just below gale force Mon afternoon as the strong high pressure over Mexico shifts eastward and weakens. Seas with this event will subside to 9 to 13 ft on Mon and to less than 8 ft on Tue as the northerly winds diminish to 20 kt or less. Please refer to the latest high seas forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more specific marine related details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 08N75W TO 06.5N88.5W, where latest scatterometer data indicated that it transitions to the ITCZ and continues to 05.5N102W TO 05.5N130W TO beyond 06N140W. Scattered moderate to strong convection is within 210 nm N and 120 nm S of the ITCZ between 116W and 130W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... At the surface, a weak ridge will prevail over the area through Mon morning to maintain light to gentle breezes across the area waters. Northwest swell with seas 8 to 10 ft will dominate the offshore waters of Baja California through early Mon morning before briefly subsiding to 6 to 8 ft through noon on Mon. A deep layered upper level low has moved eastward across Baja California Norte and the far northern Gulf of California today, and is bringing broken to overcast middle to high clouds across Baja California Sur and the adjacent western States of Mexico. Some light to moderate rain and elevated thunderstorms embedded in this cloud cover will gradually shift NE across the Gulf of California and across northern Mexico through Mon. A cold front will move eastward into the area by early Mon afternoon, followed by moderate high pressure and freshening northerly winds across the offshore waters. This pattern will prevail through early Wed before the ridge begins to weaken. Also accompanying the front will be a new pulse of large NW swell. Seas across the northern waters will build to 9 to 15 ft around midday Mon and then 12-18 ft late Mon night, and 8-12 ft across the waters of Baja California Sur. This swell event will peak early Tue and continue throughout the day across the Baja waters, with seas to 10 ft and greater reaching 105W Wed morning. Swell of this size and period will produce hazardous seas for mariners, and create very large and powerful surf along the Pacific reefs and beaches. This strong high surf will produce coastal flooding and beach erosion in many exposed locations from southern California to western Mexico. Across the Gulf of California, strong high pressure north of region have been supporting moderate to fresh breezes across the basin. Strong high pressure will build north of the area by Wed, and will support fresh to strong winds across the northern and central gulf. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo...Strong NE winds with gusts to gale force across the Gulf this morning have diminished slightly early this afternoon and will persist through this evening. These strong gap winds will continue into mid week, pulsing to strong during the overnight and early morning hours through Tue then remain fresh through Wed. Seas downwind of the Gulf will remain around 8 to 9 ft, and peak near 10 ft during the times of peak nocturnal winds. Fresh NE winds will also pulse across the major gap wind zones from Gulf of Panama to the Gulf of Fonseca through Mon night. Elsewhere, gentle to moderate winds will persist on either side of the monsoon trough through early next week, as seas remain in the 4 to 6 ft range. REMAINDER OF THE AREA... A broad mid to upper-level trough stretches from the upper-level low over Baja California to 23N117W and to near 17N122W. This feature has helped to support scattered moderate convection north of the ITCZ to near 15N and between 115W and 130W. A 1022 mb high near 28N122W is producing a modest pressure gradient to the south between it and the ITCZ. Afternoon scatterometer data showed moderate to fresh NE tradewinds to the south of 22N and west of 115W, with stronger winds south of 10N in the zone of convection. A cold front has moved into the northwest corner of discussion area and extends from 30N133W TO 27N140W. This front will move eastward across the waters north of 20N through Mon while weakening. The main impact will be a pulse of large NW swell. Recent satellite altimeter data showed seas of 15-25 ft behind the front, and 9-15 ft just ahead of the front. This swell will move into California and Baja California this evening through Mon and produce high seas and large dangerous surf. $$ Stripling