000 AXPZ20 KNHC 290342 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Fri Dec 29 2017 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 0000 UTC surface analysis and satellite imagery through 0300 UTC. ..SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A tight pressure gradient related to strong ridging over eastern Mexico and the western Gulf of Mexico will continue to support gale northerly winds southward over the Gulf of Tehuantepec waters through early on Saturday morning. Maximum waveheights resulting from these will reach the range of 10-15 ft within about 30 nm either side of a line from 16N95W to 14N95.5W early on Friday subsiding to 9-12 ft by early on Saturday. Seas of 8-9 ft will propagate downstream from the Gulf of Tehuantepec region in a mixed NW and NE swell, and are expected to reach S to near 10N and westward to near 100W Friday and Saturday. Winds and seas diminish on Saturday as the high pressure N of the area weakens. Refer to the latest high seas forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more details. Beyond Saturday, global model guidance continues to suggest that a strong cold front will sweep through the Gulf of Mexico late Sunday into early Monday followed by strong high pressure ridging that surges southward along the Sierra Madre Oriental mountains, with the associated tight pressure gradient bringing strong gale force or even storm force winds through the Gulf of Tehuantepec by Monday night and into Tue morning. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough axis extends from a 1008 mb low at 05N79W to 07N90W to 05N100W to 06N107W, where it transitions to the intertropical convergence zone and continues to 09N111W and to 09N120W where it ends. It resumes at 09N130W to beyond the area at 09N140W. Scattered moderate convection is noted from 08N to 11N between 114W and 119W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please refer to the special features section above for details on an ongoing Gulf of Tehuantepec Gale event. A fairly tranquil synoptic pattern associated with a nearly stationary subtropical high west of California and a surface ridge extending SE from the high will persist for several days. This will maintain gentle to moderate NW to N winds off Mexico through the weekend. Seas will be in the general range of 4-6 ft over the offshore waters and 2-4 ft in the Gulf of California. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... A moderate high pressure gradient in the western Caribbean will continue to support pulsing fresh to strong NE winds from 09N to 11N east of 90W, including Gulf of Papagayo, through Tuesday night with seas to 7-9 ft primarily from NE wind waves. Mainly gentle winds are expected elsewhere through the weekend, with offshore seas generally 4-5 ft. REMAINDER OF THE AREA... Long-period NW swell is producing 8-9 ft seas from 15N to 25N west of 125W. Seas will continue to gradually diminish through this evening s the peak swell continues to propagate to the SE. Divergence aloft to the SE of an upper trough along 120W along with jetstream dynamics, and with the presence of fresh trade winds in the lower levels are factors that have come together to support scattered showers and thunderstorms from 09N to 13N between 112W and 118W. An associated surface trough and weak low pressure along the intertropical convergence zone near 10N125.5W will drift westward over the next 48 hours then dissipate. The gradient between the trough and high pressure over northern waters tightened during Thursday afternoon, and this led to trade winds increasing to the 20-25 kt range over the waters from 15N- 19N between 121W-127W along with seas of 8-9 ft from a combination of NW swell and wind waves. The Ascat pass from Thursday afternoon across this area nicely highlighted these winds. These strong winds will diminishing to the 15-20 kt Friday afternoon. Seas to 8 ft in a decaying NW swell are expected from 15N-19N between 121W-127W on Friday. These seas will subside to 6-7 ft Friday evening and to 5-6 ft on Saturday. $$ Aguirre