678 AXPZ20 KNHC 151557 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Fri Dec 15 2023 Tropical Weather Discussion for the eastern Pacific Ocean from 03.4S to 30N, east of 120W including the Gulf of California, and from the Equator to 30N, between 120W and 140W. The following information is based on satellite imagery, weather observations, radar, and meteorological analysis. Based on 1200 UTC surface analysis and satellite imagery through 1500 UTC. ...SPECIAL FEATURES... Tehuantepec Gale Warning: Gap winds in the Gulf of Tehuantepec region have diminished to just below gale-force per latest scatterometer pass that shows northerly winds of 20-30 kt. Seas with these winds are 8-11 ft. These winds extend downstream from the Gulf to near 11N97W. Strong to near gale-force winds will continue into the weekend, with gale force winds returning on early Sat evening. This next round of gale force winds is expected to last through the weekend, and continue into early next week. Rough to very rough seas are expected. NW Eastern Pacific Gale Warning: Deepening low pressure of 992 mb is N of the area near 34N137W. A cold front extends from the low to 30N135W and to 21N140W. A tight pressure gradient between the front and high pressure west of southern California supports gale force southerly winds N of 28N E of front to about 132W. Seas with these winds are 10-13 ft. Another cold front will enter the forecast waters from the same extratropical low on Sat, bringing another round of gale-force winds. Expect these winds to occur north of 28N and west of 136W. These gale force winds will diminish to just below gale-force on Sat night, with strong winds continuing across the northwest waters through Sun. Very large northwest swell propagating through the northwest forecast waters will produce 12 ft and greater seas through the weekend and into early on Mon. Seas of 17-20 ft are forecast for that part of the area from Sat through early on Sun. Hazardous marine conditions are occurring. The leading edge of the 12 ft and greater seas will reach as far south as 15N and west of about 129W by late on Sun. Seas will begin to slowly subside starting Sun afternoon and into early next week. Please read the latest High Seas Forecast and the Offshore Waters Forecast issued by the National Hurricane Center at https://www.nhc.noaa.gov/text/MIAHSFEP2.shtml and www.nhc.noaa.gov/marine/offshores.php for details on both of these special features. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from northern Colombia near 10N74W to 06N90W to 05N110W. The ITCZ continues from 05N110W to 09N125W to beyond 09N140W. Scattered moderate to isolated strong convection is noted from 03N to 08N between the coast of Colombia and 108W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please refer to the Special Features section for details on a Gale Warning for the Gulf of Tehuantepec region. The combination of high pressure over the U.S. Great Basin and relatively lower pressure over northwest Mexico and the Gulf of California area is allowing for mostly fresh to strong northwest to north winds over the Gulf of California with seas to 6 ft. Meanwhile, weak pressure gradient dominates the Mexican offshore waters, outside of the Gulf of Tehuantepec. Moderate or weaker winds and slight to moderate seas continue across the rest of the offshore waters. Seas across the Baja California offshore waters and over the southern Mexico offshore waters are in the 4-6 ft range due to long-period west to northwest swell. No significant convection is presently noted over these waters. For the forecast, strong to near-gale force northerly gap winds will continue through Sat morning, before increasing back to gale force in the afternoon. These winds are forecast to remain at gale force speeds into early next week. Rough to possibly very rough seas can be expected with these winds. Meanwhile, high pressure will build over the Great Basin in the western United States through Sat. The associated gradient will maintain fresh to strong northwest winds over the Gulf of California through tonight, then diminish Sat through Sun night. The weakening of these winds may occur a little sooner. ...OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... The combination off strong high pressure that stretches from the eastern United States southwestward to southeastern Mexico and relatively lower pressure found south of Mexico is maintaining fresh to strong trade winds in the Gulf of Papagayo region, including the coast of southern Nicaragua. These winds extend westward to near 09N89W. Seas with these winds are in the range of 5-8 ft. In addition, seas to 9 ft in a northwest swell generated by the Gulf of Tehuantepec gap wind event will continue today over the offshore waters of Guatemala and El Salvador, then subside to 5-7 ft tonight. The aforementioned strong pressure gradient is also supporting moderate to fresh northerly winds in the Gulf of Panama. These winds reach south to near 06N. Seas over these waters are 4-6 ft. South of 06N, mostly gentle south to southwest winds are occurring, with seas of 4-5 ft due to mixed swell. For the forecast, the fresh to strong northeast to east winds in the Gulf of Papagayo will diminish to moderate to fresh speeds by early this evening. These winds will increase back to fresh to strong beginning late Sun and continue through mid week while expanding to the southwest. The large northwest swell over the Guatemala and El Salvador offshore waters will subside today. Expect rough seas in this area once again for Sun and Sun night due to another Gulf of Tehuantepec gap wind event that begins on Sat. Elsewhere, winds are moderate or weaker for the next several days. ...REMAINDER OF THE AREA... Please see the Special Features section for more information on the gale warning for the far northwest waters of the area. Outside the near gale to gale-force winds described above under Special Features, fresh to strong south to southwest winds that are over the northwest part of the area in advance of a strong frontal system are located to the northwest of a line from 30N130W to 25N135W and to 23N140W. Overnight ASCAT data passes from 0521Z and 0626Z nicely captured these winds. Seas with these winds are 10-12 ft. Overnight altimeter data passes indicated seas to 11 ft near 29N134W. A 1022 mb high center is analyzed just west of southern California. The associated gradient controls the wind regime over most of the tropical eastern Pacific. Moderate to fresh trade winds are noted from the ITCZ north to 20N. Seas over these waters are 5-7 ft. Moderate to fresh southeast winds are south of 03N and west of 125W. Seas over these waters are also 5-7 ft. Light to gentle winds and moderate seas are present elsewhere. For the forecast, trade winds will slowly diminish to be moderate or weaker today and through the weekend as the gradient from high pressure that is over the eastern and central sections of the area slackens in response to frontal systems moving into the northwest part of the discussion area. $$ GR