000 AXPZ20 KNHC 161541 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 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 120 UTC surface analysis and satellite imagery through 1520 UTC. ...SPECIAL FEATURES... Gale Warning South of Southwestern Mexico (EP90): A broad 1007 mb area of low pressure located a few hundred nautical miles offshore of the SW coast of Mexico near 11.5N102W, is producing showers and thunderstorms and is gradually becoming better organized. Numerous moderate and isolated strong convection is noted within 300 nm in the N semicircle and 120 nm in the S 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 likely to form within the next day or two. This system is expected to move slowly W and then turn NW late in the week offshore of the coast of SW 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 night. 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, and seas of 8-13 ft, in the Gulf of Tehuantepec. Seas will peak near 15-16 ft tonight as winds peak near 40 kt. The area of high pressure will start to shift eastward. This will loosen the pressure gradient which will help diminish winds below gale-force late Tue night into Wed morning. Meanwhile, seas in the Tehuantepec region will subside below 12 ft by Tue night. The pressure gradient will remain tight enough to support pulsing fresh to strong winds through the remainder of next week. 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 11N73W to along the coast of El Salvador to the area of low pressure (EP90) near 11.5N5N102W to 07N130W to 12N140W. Scattered moderate isolated strong convection is noted S of the monsoon trough to 01N and E of 93W. Similar convection is noted from 03N to 10N between 99W and 140W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see 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, that is being monitored for TC 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 Tue night into 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. Large NW swell is forecast to spread offshore Baja California by the end of the week. 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 could 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 medium 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 today through Tue 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 today. Winds will pulse moderate to fresh, locally strong, near the Gulf of Papagayo Tue through Wed night. Gentle to moderate winds will prevail south of the monsoon trough. 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 could 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 medium chance in the next 7 days. ...REMAINDER OF THE AREA... A 1018 mb high pressure center near 28N129W 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 cold front from 30N137W to 28N140W, is propagating across the NW waters bringing seas of 8-9 ft over the NW waters out just ahead of the front. Elsewhere, seas of 5-7 ft prevail, locally 8 ft near 16N138W. 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 large 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 14-15 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. $$ Lewitsky