000 AXPZ20 KNHC 180914 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 914 UTC Tue Dec 18 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 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A scatterometer satellite pass from 0318 UTC showed gap winds were still reaching 35 kt into the Gulf of Tehuantepec, between high pressure north of the area and relatively lower pressure over the eastern Pacific. The high pressure is moving eastward, allowing gap winds into the Gulf of Tehuantepec to finally diminish below gale force early this morning. Winds will diminish further to below 20 kt by late today, as seas subside from 11 to ft less than 8 ft. Light to gentle breezes will persist into Thu, followed by another gale event by late Thu as a strong cold front pushes across the Gulf of Mexico north of the area. Strong gales with seas reaching as high as 18 ft will persist through late Fri and early Sat before gradually diminishing. 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... No monsoon trough is observed. A weak trough extends from 06N95W to 07N120W to 09N140W. Scattered moderate convection is noted from 05N to 08N between 108W and 113W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A trough reaching from 32N118W to 27N127W is sliding eastward across the northern waters toward Baja California Norte. The front will become diffuse through early today, and be 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 is very large NW swell, with the leading edge of 12 ft seas or greater impacting the northern coast of Baja California Norte. Seas of 12 ft or greater in NW swell will reach the length of the coast of Baja California Sur and the Revillagigedo Islands by this afternoon. 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 high surf will also produce coastal flooding and beach erosion in many exposed locations from southern California to western Mexico. This swell will decay to 8 to 10 ft by late Wed, just ahead of another round of NW swell to 12 ft reaching Guadalupe Island and the northern coast of Baja California by late Thu. This swell will also decay below 12 ft rapidly, leaving 8 to 10 ft NW swell in place for the Mexican open waters west of 105W through Sat. Across the Gulf of California, strong high pressure will build over the Great Basin by Wed. The high will support fresh to strong winds across the northern and central Gulf Wed through Thu, while seas build to 5- 8 ft. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... The pressure gradient between a wedge of high pressure extending from the Caribbean over Central America and lower pressure over the eastern Pacific will continue to support fresh to strong gap winds across Papagayo and other typical gap wind zones of central America until tonight, then winds will slacken as the high over the Caribbean shifts E. Farther south, fresh to strong trade winds across the southwest Caribbean will support fresh gap winds over the Gulf of Panama through tonight. Winds during this time frame could possibly pulse to strong off the Azuero Peninsula. 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... An upper-level trough extending from northern Baja California Norte to 10N135W is supporting a persistent surface trough along roughly 132W from 06N to 17N. The combination of lower level trade wind convergence and divergence aloft on the east side of the upper trough is supporting scattered convection from 13N to 16N between 113W and 117W. Farther N, a 1025 mb high is centered along 31N130W, behind the trough approaching Baja California Norte. This high will meander about this area for the next few days and maintain a modest pressure gradient to the south and southwest, to produce fresh to locally strong NE to E tradewinds between 10N and 20N to the W of 110W. Large NW swell moving through this area will produce rough seas of 10-15 ft today before seas subside very slowly through Thu. An area of confused seas running 8 to 10 ft lingers in the area from 02N to 15N between 93W and 112W. The seas in this area are primarily a mix of NW swell with shorter period NE and E swell from ongoing Mexican and Central American gap wind events. This area will gradually diminish to 8 to 9 ft west of 100W by mid week in predominantly NW swell as it merges with the larger area of NW swell approaching from the west. $$ Christensen