000 AXPZ20 KNHC 171603 TWDEP Tropical Weather Discussion...Updated NWS National Hurricane Center Miami FL 1605 UTC Tue Oct 17 2023 Updated to change Gale to Storm Warning for EP90 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 1430 UTC. ...SPECIAL FEATURES... Storm Warning South of Southwestern Mexico (EP90): Showers and thunderstorms associated with an 1005 mb area of low pressure located a few hundred nautical miles offshore of the southwestern coast of Mexico near 12.5N106W are gradually becoming better organized, but the low still does not have a well-defined center. Numerous moderate isolated strong convection is noted from 10N to 19N between 98W and 110W. Associated winds are currently 20-30 kt with seas of 8-11 ft. Environmental conditions are conducive for further development of this system, and a tropical depression is very likely to form later today or tonight. This system is expected to move slowly west- northwestward and then turn northwestward or northward late in the week offshore of the coast of southwestern Mexico. This system has a high chance of tropical cyclone development in the next 48 hours. Gale-force winds are forecast beginning late this afternoon, then increasing to storm force by early Thu. Please read the latest NHC Tropical Weather Outlook at www.hurricanes.gov and the latest NHC High Seas Forecast at www.hurricanes.gov/marine for more details. Gulf of Tehuantepec Gale Warning: The pressure gradient between high pressure along the eastern slopes of Mexico and the eastern north Pacific monsoon trough is supporting gale-force gap winds, up to 40 kt. Peak seas are likely reaching near 15-16 ft with these winds. The area of high pressure will start to shift eastward tonight. This will loosen the pressure gradient which will help diminish winds below gale-force by Wed afternoon when seas will also likely subside below 12 ft. The pressure gradient will remain tight enough to support pulsing fresh to strong winds through the remainder of the week. Please read the latest NHC High Seas Forecast at website www.hurricanes.gov/marine for more details. NW Swell in the NW waters: Large NW swell will push SE of 30N140W tonight building seas to 12 ft or greater N of 25N and W of 135W by early Wed afternoon. Seas will peak around 15 ft Wed afternoon into the evening near 30N140W. This swell will continue to spread SE with seas 8 ft or greater covering the majority of the waters W of 100W by the end of the week, when peak seas should subside to just below 12 ft. Seas will continue to gradually decay through the upcoming weekend. Please read the latest NHC High Seas Forecast at website www.hurricanes.gov/marine for more details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 10N73W to the Gulf of Papagayo near 11N86W to low pressure (EP90) near 12.5N106W to 08N115W to 11N133W to 08N134W to 11N140W. Scattered moderate isolated strong convection is noted from 02N to 06N between 77W and 82W, from 05N to 15N between 83W and 96W, from 04N to 10N between 100W and 124W, and from 10N to 12N between 120W and 129W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the SPECIAL FEATURES section above for more on the ongoing Gulf of Tehuantepec gale-force gap wind event and a Gale Warning in effect for EP90 near 12.5N106W, that is being monitored for tropical cyclone development. Aside from the Gulf of Tehuantepec and EP90, a ridge extends across the Baja California offshore waters. Gentle to moderate winds prevail west of the Baja California peninsula as well as the Gulf of California. Light to gentle winds are noted off SW Mexico. Seas are in the 4-6 ft range over the open waters off Mexico, except 6-7 ft offshore Baja California, and 1-3 ft over the Gulf of California. For the forecast, gale-force gap winds will prevail over the Gulf of Tehuantepec through Wed morning. Fresh to strong winds will continue to pulse over the Tehuantepec region through the remainder of the week. Rough to very rough seas can be expected over this area through Wed. Gentle to moderate winds will prevail elsewhere through the end of the week. Fresh to strong winds offshore Baja California may develop this weekend. Large NW swell is forecast to spread offshore Baja California by the end of the week into the weekend. Looking ahead, an area of low pres is expected to form S of the coasts of Guatemala and southern Mexico in a couple of days. Gradual development of the disturbance is expected, and a tropical depression is likely to form late this week or over the weekend while the system meanders over the far eastern portion of the basin. This system has a low chance of tropical cyclone formation in 48 hours and a high chance in the next 7 days. ...OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Light to gentle winds are noted N of the monsoon trough, except locally fresh to strong downwind of the Gulf of Fonseca where numerous showers and thunderstorms are occurring. Gentle to locally moderate winds S of the monsoon trough. Seas are in the 6-9 ft range well offshore Guatemala, and in the 3-5 ft range elsewhere across the discussion waters. For the forecast, moderate to rough seas from swell generated by the Gulf of Tehuantepec gale-force gap wind event will prevail well offshore of Guatemala until early Wed. Winds will pulse moderate to fresh, locally strong, near the Gulf of Papagayo at night through Thu night. Gentle to moderate winds will prevail south of the monsoon trough. Seas may build slightly in SW swell offshore Ecuador to the Galapagos Islands by the end of the week into the weekend. Looking ahead, an area of low pres is expected to form S of the coasts of Guatemala and southern Mexico in a couple of days. Gradual development of the disturbance is expected, and a tropical depression is likely to form late this week or over the weekend while the system meanders over the far eastern portion of the basin. This system has a low chance of tropical cyclone formation in 48 hours and a high chance in the next 7 days. ...REMAINDER OF THE AREA... Please see the SPECIAL FEATURES section above for more on a Gale Warning in effect for an area of low pressure, EP90, near 12.5N106W that is being monitored for tropical cyclone development, and for details on a large NW swell event over the NW waters. A 1019 mb high pressure center near 28N133W extends a ridge to near the Revillagigedo Islands. Light winds are in the vicinity of the high center. Gentle to moderate winds are elsewhere over the discussion waters. NW swell is propagating across the NW waters bringing seas of 7-9 ft N of 10N and W of 130W, with a separate area of fresh NW swell propagating from offshore southern California to 26N between 118W and 123W. Elsewhere, seas of 5-7 ft prevail. For the forecast, the NW swell will subside this afternoon. A larger set of NW swell is expected to move into the NW waters tonight, with seas peaking near 13-15 ft on Wed and Wed night. Seas greater than 8 ft associated to this swell will merge with seas generated by EP90 to cover much of the discussion waters W of 100W by the end of the week. Meanwhile, southerly swell of 8 ft or greater will spread N of the Equator mid-week through the end of the week. Seas will gradually subside from west to east over the waters W of 125W Fri night through the weekend. $$ Lewitsky