000 AXPZ20 KNHC 162013 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Mon Oct 16 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 1800 UTC surface analysis and satellite imagery through 1800 UTC. ...SPECIAL FEATURES... Gale Warning South of Southwestern Mexico (EP90): An area of low pressure located a few hundred nautical miles offshore of the southwestern coast of Mexico near 11.5N103W is producing showers and thunderstorms that have become better organized since yesterday. Numerous moderate and isolated strong convection is noted within 360 nm in the NW semicircle and 120 nm in the SE semicircle of the low. Associated winds are currently 20-30 kt, with seas of 7-10 ft. Environmental conditions are conducive for further development of this system, and a tropical depression is very likely to form within the next day or so. This system is expected to move slowly westward and then turn northwestward 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. A gale warning is now in effect for this system beginning Tue afternoon. 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, in the wake of a cold front which moved through the Gulf of Mexico, and the eastern north Pacific monsoon trough is supporting gale-force gap winds. A recent ASCAT scatterometer pass clearly showed 30-40 kt winds there. Seas are likely 10-15 ft with these winds. The area of high pressure will start to shift eastward. This will loosen the pressure gradient which will help diminish winds below gale-force Wed morning 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 through the week building seas to 12 ft or greater N of 25N and W of 135W by early Wed afternoon. Seas will peak around 15 ft then near 30N140W. These seas will continue to spread SE with 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 less than 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 11N74W to along the coast of El Salvador to the area of low pressure (EP90) near 11.5N113W to 07N130W to 13N140W. Scattered moderate isolated strong convection is noted within 360 nm offshore Colombia and Central America. Similar convection is noted from 04N to 08N between 99W and 140W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the SPECIAL FEATURES section above for more on the upcoming Gulf of Tehuantepec gale-force gap wind event and a new Gale Warning in effect for EP90 near 11.5N103W, 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 5-7 ft offshore Baja California, and 2-4 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 west of the Baja California peninsula and over Gulf of California will continue through Tue night before diminishing. 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 pressure is expected to form south of the coasts of Guatemala and southern Mexico in a few days. Gradual development of the disturbance will be possible, 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, with gentle to locally moderate winds S of the monsoon trough. Seas are in the 3-5 ft range across the discussion waters. For the forecast, seas will increase moderate to rough tonight through Tue night well offshore of Guatemala from swell generated from the Gulf of Tehuantepec gale-force gap wind event. Light to gentle winds will prevail north of the monsoon trough this evening. Winds will pulse moderate to fresh, locally strong, near the Gulf of Papagayo late tonight 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 pressure is expected to form south of the coasts of Guatemala and southern Mexico in a few days. Gradual development of the disturbance will be possible, 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 11.5N103W that is being monitored for tropical cyclone development, and for details on a large NW swell event over the NW waters. A high pressure center near 28.5N130W extends a ridge to near the Revillagigedo Islands. Light winds are in the vicinity of the high center. Gentle to moderate winds are elsewhere N of the monsoon trough. South of the monsoon trough, mainly light to gentle winds are noted. NW swell, associated with a slowing cold front from 30N137W to 28N140W, is propagating across the NW waters bringing seas of 8-10 ft over the NW waters out just ahead of the front. Elsewhere, seas of 5-7 ft prevail, locally 8 ft from 13N to 20N to the W fo 133W. For the forecast, the NW swell will slowly propagate while subsiding the next couple of days while the cold front gradually dissipates over the northern waters. By midweek, a larger set of NW swell generated by a storm force low well NW of the area is expected to move into the NW waters, 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 W of 125W should gradually diminish this weekend. $$ Lewitsky