000 AXPZ20 KNHC 212034 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Sat Sep 21 2024 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 2030 UTC. ...SPECIAL FEATURE... A Central American Gyre is gradually developing this weekend and will continue through the middle of next week. This scenario, combined with daytime heating and orographic lifting, is expected to generate periods of excessive rainfall over southern Mexico and Central America, as well as the adjacent W Caribbean and E Pacific waters between 80W and 95W. This activity could produce dangerous flash flooding and mudslides across the area. Furthermore, strong to near gale force winds, rough seas and tstms are forecast to affect the offshore waters between Costa Rica and El Salvador from Mon night through mid week. Please follow the forecasts from your local weather offices for more detailed information. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 12N87W to 15N110W to 10N140W. Aside from the convection associated with the tropical wave/low described above, scattered moderate convection is noted within 150 nm on either side of the boundary, with the highest coverage W of 135W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A broad surface ridge extends SE to just west of the Baja California offshore waters. Moderate NW winds prevail over the Baja California offshore waters with moderate seas. Along the Gulf of California, light to gentle winds are ongoing. Light to gentle winds and slight to moderate seas are elsewhere. For the forecast, the surface ridge will remain in place and fluctuate through the weekend. Moderate to fresh NW winds will develop over the Baja California offshore waters through late tonight, then diminish to gentle to moderate speeds afterward into Wed night. Gentle NW winds will prevail across the Gulf of California through the middle of next week. An active monsoon trough will support moderate to fresh W to SW winds across the outer SW Mexican offshore waters through Mon. Looking ahead, disorganized showers and thunderstorms located a few hundred miles south of the coast of southern Mexico are associated with a trough of low pressure. Some gradual development of this system is possible while it meanders offshore through early next week, then moves slowly eastward or northeastward toward the coast of southern Mexico during the middle part of next week. Regardless of development, strong to near-gale force winds and rough seas are forecast to affect the S and SW Mexican offshore waters starting Mon night and continuing through the end of the week. ...OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate to fresh SW to W winds are ongoing south of the monsoon trough and across the offshore waters from Colombia to Costa Rica along with moderate seas. Gentle to moderate winds and slight to moderate seas prevail elsewhere. Scattered showers and tstms are over the majority of the Central America offshore waters due to an active monsoon trough. Strong winds and rough seas are likely in the regions of strongest convection. For the forecast, moderate to fresh southwest to west winds south of the monsoon trough will change little through the weekend, then increase to fresh to near gale force speeds across the offshore waters from Costa Rica to Guatemala late Mon through Wed night. Seas will build during this time in mixed swell. The monsoonal flow is expected to become very active, and dominate the region through next week. This pattern will generate increasing westerly wind waves moving into the area waters. Periods of very active weather are also expected across the Central America offshore waters through at least mid week. ...REMAINDER OF THE AREA... Surface ridging prevails across the area. The pressure gradient between the ridge and the monsoon trough to the south is resulting in moderate to fresh NE trade winds and moderate seas from 08N to 21N and W of 130W. An area of fresh to strong winds and seas to 9 ft prevails along the monsoon trough from 12N to 15N between 103W and 118W. Another area of fresh to strong winds and seas to 8 ft are noted within a 1010 mb low pres, analyzed near 11N137W. Gentle to moderate NE to E winds and moderate seas are noted elsewhere. For the forecast, the low near 137W will move W of 140W tonight. Southwest monsoonal winds will continue to become well established through the remaining weekend as the monsoon trough lifts slowly northward. Looking ahead, an area of low pressure could form well to the southwest of the southwestern coast of Mexico during the next couple of days. Environmental conditions appear conducive for some slow development of this system, and a tropical depression could form during the early or middle part of next week while the system moves slowly eastward or northeastward. Regardless of development, strong to near-gale force winds and rough seas are forecast to affect the S and SW Mexican offshore waters starting Mon night and continuing through the end of the week. $$ ERA