000 AXPZ20 KNHC 282206 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Thu Dec 28 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 1800 UTC surface analysis and satellite imagery through 2145 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 expected to reach S to near 10N and westward to near 1000W 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 05N77W to 07N90W to 06N108W, where it transitions to the intertropical convergence zone and continues west to a 1012 mb low pressure area centered near 10N125W, then farther west to beyond 07N140W. Scattered convection is noted from 10N to 15N between 110W and 120W. ...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 Monday 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 added ingredient of convergence of fresh trade winds in the lower levels are coming together to support the scattered showers and thunderstorms from 10N to 15N between 110W and 120W. A related 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 has increased trade winds enough to reach 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. These strong winds will continue into early Friday afternoon before diminishing to the 15-20 kt. Seas to 8 ft in a decaying NW swell are expected from 15N-19N between 121W- 127W on Friday, but subsiding to 6-7 ft Friday evening and to 5- 6 ft on Saturday. $$ Aguirre