000 AXPZ20 KNHC 232157 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2157 UTC Mon Dec 23 2019 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 2100 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Tight pressure gradient between high pressure centered near the eastern slopes of Mexico's Sierra Madre Oriental and low pressure of the monsoon trough in the eastern N Pacific is supporting gale force northerly gap winds in and near the Gulf of Tehuantepec, with seas to near 17 ft. As high pressure gradually weakens, this gradient will relax and winds will slowly veer and diminish, below gale force by late Tue. Swell generated from these ongoing gap winds continue to produce a large plume of 8 ft or greater seas that extends beyond 100W. Marine interests should take necessary action to avoid hazardous marine conditions over the affected waters. Please see the latest High Seas Forecast issued by the National Hurricane Center under AWIPS/WMO headers HSFEP2/FZPN03 KNHC or at website https://www.nhc.noaa.gov/text/MIAHSFEP2.shtml for further details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N83W to 06N105W. The ITCZ continues from 06N105W to 10N130W to 07N140W. Scattered moderate convection was noted within 90 nm of the ITCZ between 125W and 140W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the Special Features section above for details about the ongoing gale force gap winds across the Gulf of Tehuantepec. A cold front is analyzed from northern Baja California Norte to just east of Guadalupe Island to beyond 22N120W. Showers are probably active ahead of the front from off the northern coast of Baja California Sur to over the northern Gulf of California. Moderate SW winds are noted just ahead of the front, with moderate to fresh winds over the northern Gulf of California. Recent altimeter data shows seas around 5 to 7 ft in open waters. The front will weaken as it continues to the southeast, eventually stalling and dissipating from the central Gulf of California to through Baja California Sur by late Tue, with a secondary boundary moving through Baja California Norte and the northern Gulf of California tonight and early Tue. Strong W to NW winds will follow the first front over the waters off Baja California Sur between Punta Eugenia and Cabo San Lazaro. Long period NW swell will follow the front, impacting the open waters beyond 120 nm north of Cabo San Lazaro Tue and Wed. Farther south, the high pressure building in the wake of the front will support moderate to fresh northerly winds off Cabo Corrientes by late Tue, becoming strong by late Wed. Looking ahead, another front will move into the region starting late Wed. The front will slow and weaken as it reaches from the southern Gulf of California across Los Cabos to near Clarion Island by with an associated low pressure area moving into Baja California Norte by early Fri. Strong winds and building seas will follow the front north of Punta Eugenia. On Tue, a cold front will move through waters W of Baja California, increasing winds and seas. Expect fresh to strong W to NW winds and seas building to 9 ft. Another cold front is forecast to move across Baja California Norte into the northern Gulf of California on Thu bringing an an increase in winds and seas. A larger set of NW swell will follow the front, with seas building to 12 to 16 ft N of Punta Eugenia, and to 8 to 14 ft between Cabo San Lazaro and Punta Eugenia by Thu night. Another round of large, long-period NW swell follows the front with seas in excess of 8 ft seas over open waters reaching the Revillagigedo Islands by Fri, and lingering through Sat. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Seas generated by gales in the Tehuantepec region will continue to propagate across the offshore waters of Guatemala and El Salvador through Tue. Seas will start to subside to less than 8 ft by Tue night. Fresh to strong winds and building seas are expected across the Gulf of Papagayo and downwind to near 90W through the next several days, pulsing to near gale force during the overnight and early morning hours through at least Tue. Elsewhere, gentle to moderate south to southwest monsoon flow will persist across the offshore waters of Costa Rica, Panama, Colombia, and Ecuador, while light to gentle flow will dominate across the Gulf of Panama. REMAINDER OF THE AREA... 1010 mb low pressure is noted 30N126W with a dying front reaching southward toward 25N. A ship reported winds to 25 kt in the wake of the dying front. A recent scatterometer satellite pass showed fresh to strong northerly winds west of the low to beyond 140W, between the low pressure and 1029 mb high pressure centered well north of Hawaii. Concurrent altimeter satellite data showed seas of 8 to 11 ft in this area. A few thunderstorms are noted within 120 nm southeast of the low pressure as well. The low and front will weaken as it continues east of the area Tue, as a ridge builds across the waters north of 20N. This building ridge is already supporting fresh trades into the deep tropics west of 120W. Convergence of these trades is supporting scattered showers and a few thunderstorms along the ITCZ. A series of altimeter satellite passes over the past several hours indicated seas in excess of 8 ft over much of the region west of 120W, likely primarily in NW swell, but also including a component of shorter period NE wind waves in the area of fresh trades. Through mid week, winds will diminish north of 20N as the ridge builds eastward, but this will also allow trade winds to increase north of the ITCZ west of 125W. Looking ahead, a new cold front will move across the waters north of 25N and east of 125W from late Wed through Fri, followed by fresh to strong winds and building seas. A cold front is located over the northern waters from near 31N117W to 19N125W. Behind the front long period NW swell is contributing to seas to as high as 14 ft. This front will weaken and dissipate as it moves east. High pressure is building in the wake of the front. This has tightened the pressure gradient and increased trades across the W central waters. The fresh to strong trades will continue through at least Wed. Another surge of fresh to strong NW is accompanying a cold front that is crossing S over 31N between 125W and 140W this morning. The existing swell is expected to decay to less than 8 ft east of 125W through mid week, but will be reinforced with a new round of long period NW swell in excess of 8 ft following the next front. $$ Christensen