000 AXPZ20 KNHC 180915 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Wed Nov 18 2020 Tropical Weather Discussion for the eastern Pacific Ocean from the Equator to 32N, east of 140W. The following information is based on satellite imagery, weather observations, radar, and meteorological analysis. Based on 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Tropical Depression Twenty-One-E is centered near 15.7N 115.2W at 0900 UTC, moving WNW at 10 kt. The estimated minimum central pressure is 1007 mb. Maximum sustained winds are 30 kt with gusts to 40 kt. The system has become better organized tonight, with a small dense area of central convection, It is expected to become a tropical storm within the next 12 hours, then weaken by Thu as it encounters a more unfavorable marine environment. Numerous moderate to strong convection is within 90 nm of the center. Please read the latest High Seas Forecast issued by the National Hurricane Center at website- https://www.nhc.noaa.gov/text/MIAHSFEP2.shtml and the latest Tropical Depression Twenty-One-E NHC Forecast/ Advisory and Public Advisory at www.hurricanes.gov for more details. Tehuantepec Gale Warning: A tight pressure gradient across the western Gulf of Mexico and southern Mexico is supporting strong gales across the Tehuantepec region. This event will be long- lived, with gale force winds forecast to reach near storm force this morning, then again tonight into early Thu. Wave heights could build to 14-20 ft each night, and up to 22 ft downstream of the Gulf of Tehuantepec early this morning. Please read the latest NWS High Seas Forecast issued by the National Hurricane Center at website https://www.nhc.noaa.gov/text/MIAHSFEP2.shtml for more details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from Tropical Storm Iota in Central America near 13N89W to 10N93W to 11N97W, then resumes southwest of Tropical Depression 21E near 14N116W to 08N135W. The ITCZ continues from 08N135W to beyond 08N140W. Scattered moderate convection associated with TS Iota is north of 07N between 85W and 94W. Scattered moderate isolated strong is noted from 09N to 13N between 113W and 123W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A Gale Warning remains in effect for the Gulf of Tehuantepec. Please see the Special Features section above for details. A ridge extends across the offshore forecast waters west of Baja California, producing gentle to moderate northwesterly winds. Wave heights are 5-7 ft in long-period NW swell. This swell will continue to slowly decay today. A cold front is expected to move across Baja California Norte and the northern Gulf of California on Fri. Strong high pressure building eastward behind the front will induce fresh to strong NW winds in the northern Gulf Sat night and Sun. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and WITHIN 750 NM OF ECUADOR... Enhanced west to southwest monsoonal flow west of Costa Rica and Nicaragua is due to Tropical Storm Iota, over Central America. These winds are expected to weaken today as Iota dissipates over land. Elsewhere, moderate to fresh southwest winds are present south of the monsoon trough east of 100W, with mainly gentle west to northwest winds north of the trough. Sea heights are generally 5-7 ft. Large seas generated in the Tehuantepec region will propagate into the offshore waters of Guatemala and El Salvador through Thu. REMAINDER OF THE AREA... See the Special Features section above for details on Tropical Depression Twenty-One-E. A cold front extends across the NW part of the discussion area from 30N126W to 23N140W. The front will push eastward and weaken during the next 12-24 hours, becoming a dissipating stationary front from 30N122W to 23N140W this evening. NW swell associated with the front will propagate SE and slowly diminish through Wed. A low pressure system is expected to stall near 31N140W Thu and Fri, then shift westward on Sat as a strong ridge builds north of 30N. Tropical Depression 21E will weaken later this week as it moves westward across the region. Associated seas greater than 8 ft will persist north of the 21E remnant low due to a persistent gradient between the low and a strengthening ridge to the north. $$ Mundell