000 AXPZ20 KNHC 200305 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 022 UTC Thu Dec 20 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 0245 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A cold front is entering the Bay of Campeche. The front will continue sweeping SE across the Gulf of Mexico tonight through Thu. High pressure building S a long the Sierra Madre Oriental in the wake of the front will generate a tight pressure gradient over the area and usher in the next gale force gap wind event. Winds will rapidly increase to gale force by late Thu and to strong gale force by Fri morning. The plume of strong gap winds will reach about 500 nm to the SW of the Gulf of Tehuantepec by late Fri, with seas building as high as 19 ft within the area of strong winds. The gales will persist through Fri night, then diminish on Sat as the high pressure N of the area weakens and shifts east. Fresh to strong gap winds will then persist across the Gulf of Tehuantepec through Sun. Another gale could be on tap for the Gulf of Tehuantepec Sun night. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough extends from 06N74W to 05N79W to 06N89W to 06N97W. The ITCZ continues from 06N97W to 05N118W to beyond 08N140W. Scattered moderate and isolated strong convection is present from 05N to 10N W of 130W. Scattered moderate convection is seen from 04N to 07N between 87W and 93W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see above for more on the impending gale force gap wind event over the Gulf of Tehuantepec. Large NW swell continues to impact the forecast waters, with seas in the 9 to 13 ft range for the waters off the Baja California Peninsula to the Revillagigedo Islands. The swell in this area are beginning to decay but will remain high enough to produce hazardous seas for mariners and create large and powerful surf along the Pacific reefs and beaches. This high surf could also produce coastal flooding and beach erosion in many exposed locations from southern California to western Mexico. Another round of reinforcing NW swell to 12 ft will reach Guadalupe Island and the northern coast of Baja California Thu morning. This next batch of swell will decay below 12 ft by Thu evening as seas remain in the 8 to 10 ft range over the open waters off Mexico west of 110W through Fri. Long period NW swell along the coast of Mexico will continue to decay and allow seas to subside below 8 ft for all of the offshore waters by Sat evening. The risk of coastal flooding from high surf will diminish by Fri evening. High pressure building over the Great Basin will support fresh to strong winds along the Baja coast of the central Gulf of California through Thu morning, with seas peaking around 8 ft. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: A cold front will move across the SW Caribbean on Fri morning. Strong N winds behind the front will funnel through the Gulf of Papagayo, increasing to near gale force by late Fri night. This event will peak on Sat as winds reach minimal gale force. A tight pressure gradient between high pres building behind the front and lower pres in the SW Caribbean will support the continuation of the gap wind event through Sun night. Seas are expected to peak near 12 ft on Sat morning. Winds and seas will gradually diminish Sun night through Mon night. Fresh to locally strong N winds are expected over the Gulf of Panama Sat night through early on Mon. Winds could become strong Sat night and Sun as seas peak around 8 ft. Elsewhere, gentle to moderate winds will persist, with seas in the 4 to 7 ft range. REMAINDER OF THE AREA... High pressure of 1027 mb is centered north of the area near 34N126W. The pressure gradient between this area of high pressure and lower pressure in the vicinity of the ITCZ will support moderate to fresh trade winds north of the ITCZ to around 20N. A sharp upper-level trough near 155W will eventually cut off near 145w and induce a nearly stationary trough along the ITCZ just west of 140W by Fri afternoon. This will tighten the pressure gradient further in this area. Trade winds will increase from fresh to strong N of the ITCZ to near 15N and west of 135W late Thu through Mon night. NW swell continues to prevail across the discussion area. Seas of 8 ft or greater are noted W of 99W. Another set of NW swell has entered the NW waters, with seas of 12 to 14 ft noted NW of a line from 30N126W to 18N140W. Seas will subside N of 20N and W of 120W tonight through Sat. $$ CAM