000 AXPZ20 KNHC 161605 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 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 1200 UTC surface analysis and satellite imagery through 1545 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 is bringing strong gale force northerly winds over the Gulf of Tehuantepec with seas to 18 ft. This strong gap wind event will continue through tonight, before diminishing on Mon as the strong high pressure over Mexico shifts eastward and weakens. Seas with this event will subside to 9 to 13 ft Mon and to less than 8 ft on Tue as the northerly winds diminish to fresh speeds. 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 07N78W to 06N88W, where latest scatterometer data indicated that it transitions to the ITCZ and continues to 04N110W to 07N118W to 08N130W to 09N140W. Scattered moderate convection is within 30 nm either side of ITCZ between 116W and 121W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A weak ridge will prevail over the area maintaining light to gentle breezes across the area. Northwest swell with seas to 9 ft will continue in the offshore waters of Baja California through this evening before subsiding to 8 ft late tonight. A cold front will approach the region Mon bringing a new set of northwest swell, with seas from 12 to 17 ft reaching the northern coast of Baja California Norte and Guadalupe Island. Swell of 12 to 15 ft will cover the Baja offshore waters to the Revillagigedo Islands into Tue. Swell of this size and period could likely pose hazardous seas for mariners, while at the same time create very powerful and dangerous surf along the Pacific reefs and beaches, and is expected to produce coastal flooding and beach erosion in some locations. Over the Gulf of California, strong high pressure north of region have been supporting moderate to fresh breezes across the basin. A mid to upper-level disturbance approaching the area from the west may bring a few showers to the central and southern portions of the Baja California Peninsula and Gulf of California toda and tonight. 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 northeast winds through the Gulf this morning will become mainly fresh to strong by this evening. These winds will continue into mid week, pulsing to strong during the overnight and early morning hours through Tue then to fresh speeds through Wed. Seas with these winds are expected to be 8 to 9 ft. Fresh winds will also pulse across the Gulf of Panama and 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 a mid to upper- level low over far northern Baja California to 23N117W and to near 17N122W. A very strong jet stream branch rounds the base of this trough and extends northeastward to over northwestern Mexico. The combined factors of upper-level divergence to the east and southeast of the trough and jet dynamics aloft in combination with trade wind convergence in the lower atmospheric levels are supporting scattered moderate convection north of the ITCZ to near 15N and between 125W and 130W. Areas of moderate rain with possible embedded isolated thunderstorms are evident from 15N to 21N between 115W, while mostly rain is possible from 18N to 24N east of 115W to central and southern Baja California. Ascat data from overnight last night highlighted fresh to strong east winds near 13N130W. A concurrent altimeter satellite pass showed seas to 9 ft, likely mixed with northwest swell. A cold front has moved into the northwest corner of discussion area. This front and move eastward across the waters north of 20N through Mon afternoon while weakening. The main impact will be a new set of northwest swell, with combined seas in excess of 12 ft to as high as 22 ft propagating across most of the region north of 12N and west of 120W through late Mon. During the early to middle part of next week, the leading edge of this next round of northwest swell will mix with shorter period northeast and east swell emerging from the gap wind areas, and possibly even southerly swell, to create an area of mixed seas west of about 107W. $$ Aguirre