000 AXPZ20 KNHC 172159 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Mon Dec 17 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 pressure gradient over SE Mexico between high pressure along the E slopes of the Sierra Madre Orientales and lower pressure in the vicinity of the ITCZ remains strong enough to produce minimal gale force N winds over the Gulf of Tehuantepec and extending downstream to near 14.5N95.5W. Corresponding maximum seas have subsided slightly to around 12 ft. These gap winds will diminish slight to at or just below gale force this evening as the strong high pressure over Mexico shifts eastward and weakens. However, nocturnal drainage flow typically increases winds 3-5 kt and will restore minimal gales to the Gulf of Tehuantepec overnight, ending just before sunrise. Seas in the Gulf will subside to between 8 and 11 ft by this evening and to less than 8 ft on Tue as the winds diminish to 20 kt or less. 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 significant monsoon trough was observed. The ITCZ extends from 05N89W to 04N94W to 05N101W to 05N113W to 08N123W to 05N132W to beyond 04N140W. Scattered moderate and isolated strong convection was seen from 03N to 08N between 92W and 117W. Scattered moderate convection was noted from 05N to 11N between 120W and 128W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A weak cold front will move eastward into north portions of the area this evening, then will 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 will be a new pulse of large NW swell, with the leading edge of 12 ft seas or greater reaching the northern coast of Baja California Norte and Guadalupe Island by this evening. The long period NW swell will bring sea heights of 12 to 16 ft across most of the waters off Baja California and southward to beyond the the Revillagigedo Islands. 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 through 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 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 131W 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 130W. Farther N, a weakening frontal boundary analyzed from 30N123W to 28.5N130W to 25N140W is expected to become diffuse as the northern portion moves eastward toward Baja California tonight and across north portions of the penisula Tue morning. A new round of long period NW swell is outrunning the front eastward, with the leading edge of 12 ft seas approaching Guadeloupe Island and the coast of Baja California Norte. The NW swell will continue to move eastward, with 12 ft seas dominating most of the area west of 120W and north of 05N by late Tue. 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