000 AXPZ20 KNHC 170922 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Sat Oct 17 2020 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 0600 UTC surface analysis and satellite imagery through 0830 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: High pressure building across the Gulf of Mexico north of the region has forced strong northerly gap winds across the Gulf of Tehuantepec since late Fri afternoon. These winds have since increased to gale force from the coast to about 15N, and will increase slightly and extend farther downwind overnight. These gale force winds are expected to persist through Sat and slowly diminish below gale force early Sat night. Seas are building downstream accordingly, and are estimated to be near 11 ft at this time and will build to 14-15 ft by Sat morning. Strong gap winds will continue to pulse through the Gulf of Tehuantepec with seas to 8 ft Sun night through the early part of the week. ...TROPICAL WAVES... A tropical wave axis is near 102W from 07N to 16N, moving W at 10-15 kt. Associated convection is described below. A tropical wave axis is near 132W from 06N to 18N, moving W at 5-10 kt. Associated 1009 mb surface low pressure is near 13N132W. Scattered moderate to strong convection is observed from 10N to 15N between 129W and 134W, while scattered moderate convection is from 16N to 19N between 122W and 130W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from near 11N72W to 09N79W to 11N85W to 08N107W to 1009 mb low pressure near 12N131.5W to 11N135W. The ITCZ axis extends from 11N135W to to 10.5N140W. Scattered moderate isolated strong convection is noted from 06N to 13N between 91W and 122W, and within 150 nm of the coastline between 87W to 101W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the Special Features section for more details on the developing Gale Warning in the Gulf of Tehuantepec. 1015 mb high pressure is centered west of Baja California near 25N122W. The pressure gradient between the high pressure and lower pressure over the Sonoran desert is supporting moderate to fresh NW winds across the offshore waters of central Baja California and central portions of the Gulf of California, as confirmed by recent scatterometer satellite passes. Farther south, with exception of the Gulf of Tehuantepec, gentle to moderate breezes persist. Recent altimeter data indicated 4 to 6 ft over open waters, except to 7 ft just north of Punta Eugenia. This is generally in NW swell off Baja California and SW swell farther south. Farther south, minimal gale force prevail across the Gulf of Tehuantepec. The high pressure west of Baja California will maintain mostly moderate NW across the waters north of 20N into Sun. NW winds off Baja California Norte will develop late Sun into Tue as low pressure deepens slightly over the southwest U.S. and high pressure builds to the west. Farther south, new longer period SW swell will reach the Mexican offshore waters south of 20N by late Mon, mixing with seas still emerging from the Gulf of Tehuantepec, and eventually mixing with NW swell off Baja California by late Tue. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and WITHIN 750 NM OF ECUADOR... Gentle to moderate easterly trade winds are noted north of the monsoon trough and west of 90W, with moderate to fresh SW winds farther south from Ecuador to Costa Rica. Seas are 5 to 7 ft primarily in SW swell. A few clusters of showers and thunderstorms are evident along the monsoon trough across Panama and Costa Rica. The pressure gradient is subtly tightening across the southwest Caribbean, southern Central America and the tropical eastern Pacific as high pressure builds north of the area. This is supporting moderate to fresh gap winds through the Gulf of Papagayo and off southern Nicaragua tonight and is expected to pulse to pulse to fresh again Sat night. Meanwhile, SW winds will increase slightly off Panama as pressure lowers over the southwest Caribbean. These increased winds will coincide with the arrival of new longer period SW swell into the waters off Central America, allowing combined seas to reach 8 ft south of Panama by Mon. REMAINDER OF THE AREA... The pressure pattern remains fairly amplified north of 20N, with a mid/upper low centered near 28N127W and a mid/upper anticyclone centered farther west of northern Mexico. This pattern is supporting the 1015 mb surface high near 25N122W and a surface trough farther west along 127W/129W from 20N to 27N. Farther south, a tropical wave along 132W has temporarily come into phase with the southern portion of the surface trough. Recent scatterometer data indicated a surface low persists where the tropical wave intersects the monsoon trough near 13N132W. Active weather is occurring within 240 nm southeast through southwest of this low pressure. The low is moving west with the tropical wave, and will gradually open into a trough by Mon as it moves to the WNW, following behind the surface trough to it's north. However, the dry and subsident northerly deep layer flow over the region west of 130W is unfavorable for much further development at this time. High pressure will build north of 20N in the wake of the troughs, supporting fresh trade winds early next week from roughly 15N to 25N mainly west of 125W. Farther east, seas will reach 8 ft Sat into Mon near the monsoon trough east of 110W, due in part to fresh northerly swell emerging out of the Gulf of Tehuantepec and new longer period SW swell moving into the area. $$ Stripling