000 AXPZ20 KNHC 170335 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 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 0000 UTC surface analysis and satellite imagery through 0300 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Strong northerly gap winds across the Gulf of Tehuantepec this evening have recently increased to gale force from the coast to 15N. High pressure building across the Gulf of Mexico north of the region will further increase the areal extent of these gale force winds overnight, and will persist through early Sat night. Seas will build downstream accordingly, reaching up to 15 ft by Sat morning. Winds will diminish below gale force by early Sun, but strong gap winds will continue to pulse through the Gulf of Tehuantepec with seas to 8 ft through the early part of the week. ...TROPICAL WAVES... A tropical wave axis is near 101W from 04N to 17N, moving W at 10-15 kt. Associated convection is described below. A tropical wave axis is near 132W from 04N to 19N, moving W at 10 kt. Associated surface low pressure is near 12N131.5W. Scattered moderate to isolated strong convection is observed from 09.5N to 17.5N between 127.5W and 133W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from near 10.5N72W to 10N79W to 12N84W to 08N98W to 10N117W. The ITCZ axis extends from 10N117W to 1009 mb low pressure near 12N131.5W to 10.5N140W. Scattered moderate isolated strong convection is noted from 06N to 14N between 91W and 97W, and from 06N to 11N between 98W to 120W. 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 27N122W. The pressure gradient between the high pressure and lower pressure over the Sonoran desert is supporting moderate to fresh NW winds across the northern Gulf of California, as confirmed by earlier scatterometer satellite passes. Farther south, with exception of the Gulf of Tehuantepec, gentle to moderate breezes persist. Earlier altimeter passes indicated 4 to 6 ft over open waters. This is generally in NW swell off Baja California and SW swell farther south. Farther south, strong gap winds across the Gulf of Tehuantepec have increased to minimal gale force. 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, 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 showers are evident along the monsoon trough well west of the coast of northern 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 will support mainly overnight pulses of moderate to fresh gap winds through the Gulf of Papagayo and off southern Nicaragua at least tonight and 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 a new round of longer period SW swell into the waters off Central America, possibly 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 27N125W and a mid/upper anticyclone centered farther west of northern Mexico. This pattern is supporting the 1015 mb surface high near 27N122W and a surface trough farther west along 127W/128W from 20N to 28N. Farther south, a tropical wave along 131W/132W has temporarily come into phase with this surface trough. A scatterometer satellite pass from around 18 UTC indicated a surface persists where the tropical wave intersects the monsoon trough near 12N131W. A few showers and thunderstorms are active within 240 nm northeast 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 the 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