000 AXPZ20 KNHC 180335 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 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 0000 UTC surface analysis and satellite imagery through 0200 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Strong high pressure across the Gulf of Mexico the past 36 hours driving strong gales across the Gulf of Tehuantepec continues to slowly weaken this evening. Northerly winds across the Tehuantepec region has diminished to minimal gale force and extend downstream some 60-75 nm this evening. Corresponding maximum seas have subsided slightly to around 11 ft. These gap winds will hover near gale force this evening throughout the night, and then diminish to around 30 kt by sunrise. Winds and seas in the Gulf will subside to 20 kt or less and less than 8 ft on Tue. Looking ahead, another gale event is expected by Thu night as a strong cold front moves into southern Mexico. 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 06N74W TO 03.5N79W TO 05N86W. The ITCZ extends from 05N87W TO 07N124W to beyond 04N140W. Scattered moderate isolated strong convection is noted within 120 nm either side of the trough and ITCZ between 83W and 119W. Scattered moderate convection is noted from 06N to 09N between 121W and 132W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A weakening cold front is sliding eastward across the northern waters this evening and has reached from 30N120W to 24.5N140W. This front will continue eastward overnight and across Baja California Norte, and become diffuse. The front will 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 having reached the west coast of Baja California Norte late this afternoon. This long period NW swell will raise seas to 12-16 ft across most of the waters off Baja California and southward to beyond the the Revillagigedo Islands through Tue 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. The swell will decay below 12 ft Wed, ahead of a smaller reinforcing pulse of NW swell bringing sea heights back up to 12 ft for Baja California Norte Thu. Elsewhere seas in excess of 8 ft will persist for the Mexican open waters west of 105W through the end of this week. Across the Gulf of California, strong high pressure north of region is supporting moderate to fresh northerly breezes across the south half of the basin, with little change expected through Tue. 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 Tue night, 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 Tue night. 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 32N120W to 10N132W is sharpening up a bit and 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 along the intertropical convergence zone between 121W and 132W. Farther N, a 1025 mb high is centered along 32N128W this evening, behind the cold front 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 09N and 20N to the W of 110W. Large NW swell moving through this area will produce rough seas of 10-15 ft later tonight through Tue 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 W. $$ Stripling