Tropical Weather Discussion

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Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Thu Sep 18 2025 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 0000 UTC surface analysis and satellite imagery through 0200 UTC. ...SPECIAL FEATURES... Off the Coast of Southwestern Mexico (EP96): A broad area of low pressure located a few hundred miles off the coast of southwestern Mexico is producing a large area of showers and thunderstorms. Recent satellite-derived wind data indicate that the circulation appears to be becoming better organized. Environmental conditions are conducive for further development of this system, and a tropical depression is likely to form in the next day or two while it moves west-northwestward at 10 to 15 mph over the central portion of the eastern Pacific. Regardless of development, gradually increasing winds and building seas are possible offshore of SW Mexico and SSW of Baja California Sur. There is a high chance for tropical development in the next 48 hours. Please read the latest NHC Tropical Weather Outlook at website - https://www.nhc.noaa.gov/text/MIATWOEP.shtml for more details. ...TROPICAL WAVES... A tropical wave axis is near 87W to the N of 01N, moving W at 15-20 kt. Nearby convection is discussed in the ITCZ/monsoon trough section below. A tropical wave axis is near 108W, from 01N to 20N, moving slowly W at around 5 kt. Nearby convection is discussed in the ITCZ/monsoon trough section below. Please see the Special Features section above for more on the high potential of tropical cyclone formation with this tropical wave and associated low pressure, Invest EP96, along it. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 10N85W to low pres near 15N108W to 10N140W. Scattered moderate and isolated strong convection is noted N of 05N and E of 100W, and from 08N to 19N between 105W and 117W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please refer to the SPECIAL FEATURES section for information on an area being monitored for tropical formation, Invest EP96. Fresh to strong N to NE gap winds are noted across the Gulf of Tehuantepec. Moderate to fresh winds, locally strong, associated with EP96 are off the coast of SW Mexico, where seas are in the 7-9 ft range. Otherwise, gentle to moderate winds dominate the open waters off Mexico. Light to gentle winds are over the Gulf of California. Seas are in the 4-7 ft range off the Baja California peninsula, and 5-8 ft over the remainder of open waters off Mexico. Seas are in the 1-3 ft range over the Gulf of California, reaching 5 ft at the entrance of the Gulf. For the forecast, fresh to locally strong winds will pulse in the Gulf of Tehuantepec this evening into early Thu, with moderate to locally fresh winds pulsing afterwards through early Sat. Increasing winds and building seas are possible with the area of low pressure, Invest EP96, being monitored with a high chance of tropical cyclone formation. An area of fresh to locally strong winds off Baja California Norte will diminish early Thu. Winds may freshen off Baja California Norte this weekend. Winds will be moderate or weaker elsewhere with moderate to locally rough seas, except slight seas in the Gulf of California. ...OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Winds are mainly light to gentle N of the monsoon trough, with gentle to moderate winds S of the monsoon tough. Seas are in the 5-8 ft range in S to SW swell across the discussion waters. Active convection is across much of the offshore waters as described above with locally higher winds and seas possible. For the forecast, rough seas over the regional waters will gradually subside through early Thu. Moderate to locally fresh S to SW winds are expected S of the monsoon trough through early Thu, with moderate or weaker winds elsewhere and otherwise, except locally fresh near the Azuero Peninsula and Gulf of Panama Thu and locally higher near any convection. ...REMAINDER OF THE AREA... Please refer to the SPECIAL FEATURES section for information on an area being monitored for tropical formation, Invest EP96. The 1010 mb remnant low of Mario is centered near 25N119.5W. Moderate winds are in the southern semicircle of the low. Fresh NE winds, and seas of 6-7 ft, are over the NW waters. Outside of those conditions, and conditions associated with the remnants of Mario and EP96, gentle to moderate winds, and seas of 4-7 ft prevail N of the monsoon trough. Moderate to fresh winds prevail S of the monsoon trough. Seas S of the monsoon trough are in the 5-8 ft range W of 120W, and 6-9 ft range E of 120W in S to SW swell. For the forecast, the remnants of Mario will drift WNW and dissipate by Thu evening. Mainly moderate winds will prevail S of the monsoon trough, except locally fresh in the central waters near the axis through the end of the week. Rough seas in the central waters S of the monsoon trough will persist through this evening, then will consolidate around EP96, which has a high chance of tropical cyclone formation. Regardless of development of EP96, expect increasing winds and building seas in its vicinity. Freshening NE winds and building seas are expected over the NW waters into the upcoming weekend. Marine conditions may improve and be quite tranquil across the open waters by the end of the weekend and into early next week.