000 AXPZ20 KNHC 182205 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 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 1800 UTC surface analysis and satellite imagery through 2145 UTC. ...SPECIAL FEATURES... Tropical Storm Polo is centered near 16.5N 117.2W at 18/2100 UTC or 550 nm southwest of the southern tip of Baja California moving WNW at 10 kt. The estimated minimum central pressure is 1004 mb. Maximum sustained wind speed is 40 kt with gusts to 50 kt. Satellite imagery shows that the earlier observed banding features and small central dense overcast (CDO) are not presently as well defined this afternoon. The imagery shows scattered moderate convection within 90 nm of the center in E quadrant and within 30 nm of 19N116W and 14N115W. Polo is forecast to maintain is present motion through the rest of today, then turn toward the west by Thu and a westward motion through Fri. Little change in strength is expected today, with gradual weakening anticipated to begin on Thu. Polo is forecast to weaken to a depression late on Thu and degenerate into a remnant low pressure area on Fri. 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. Gulf of Tehuantepec Gale Warning: The pressure difference between strong high pressure over southern Mexico and low pressure south of Mexico is supporting strong gale force north winds across the Tehuantepec region. This event is forecast to be long-lived, with gale force winds forecast to reach near storm force this morning this evening and into early Thu. Wave heights are forecast to build to the range of 15-22 ft tonight, with the maximum of 22 ft downstream of the Gulf of Tehuantepec near 14N96W overnight tonight into early on Thu. By Thu night, the maximum wave height value is expected to be around 18 ft. The leading edge of 8 ft or greater wave heights from the generated swell is forecast to reach as far west as 110W by late Fri. 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 the remnant low of tropical cyclone Iota that is centered near 14N91W with a pressure of 1008 mb, southwestward to 10N95W to 09N100W and westward to 09N107W. It resumes at 13N117W to 10N126W and to 09N133W, where latest scatterometer data indicates that it transitions to the ITCZ to beyond the area at 08N140W. Scattered moderate convection is seen within 30 nm south of the trough between 118W-121W. 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. The gradient associated to a ridge that 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 northwest swell. This swell will decay slightly through this evening and into Thu, but will be in the same range of 5-7 ft beginning Thu afternoon. A weakening cold front that extends from southern California and well to the west of Baja California will quickly dissipate as it reaches the waters just west of Baja California Norte on Thu. In the wake of the front, strong high pressure will build eastward over the water west of Baja California, with the associated gradient expected to bring fresh to strong northwest across the northern Gulf Sat night and Sun. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and WITHIN 750 NM OF ECUADOR... 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 recently upgraded Tropical Storm Polo. A weakening cold front that is over the northwest and north- central waters along a position from 32N123W to 28N127W, then becomes stationary to 26N130W and to west of the area at 22N140W. This front will quickly dissipate as it reaches the northeast waters on Thu. An area of long-period northwest swell behind the front will shift eastward through Fri while gradually decaying. A weak low pressure system and attendant cold front will approach the far northwest part of the area near 31N140W on Thu. Its attendant cold front will weaken as it just crosses 32N140W Thu night. The front will become stationary and weaken to a trough by late Fri. An set of northwest swell will move into the northwest part of the area on Fri, with wave heights of 8-9 ft. Strong high pressure will build southward across the central and western sections of the area beginning late Fri. With this occurring, the trough will be nudged westward to just west of the northwest part of the area on Sat. The pressure gradient between the building high pressure and forecast weakening Tropical Storm Polo should allow for wave heights in the range of 7-10 ft to exist west of about 126W and from 08N to 22N from late Fri through the weekend. $$ Aguirre