000 AXPZ20 KNHC 280943 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 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 0600 UTC surface analysis and satellite imagery through 0900 UTC. ..SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A tight pressure gradient associated with high pressure ridge along the Sierra Madre Oriental mountains is inducing gale force northerly winds in the Gulf of Tehuantepec. An ASCAT pass at 0400 UTC showed a small area of 35 kt winds north of 15N between 94.5W and 95W. Model guidance indicates the pressure gradient will persist with minor variation through early Sat morning, with the main influence on wind speeds being diurnal forcing. Expect minimal gale force winds to continue over a small portion of the Gulf mainly north of 15N, but a larger area of near-gale 25-30 kt is likely north of 13N, with wind-driven seas spreading west-southwest to 100W. Looking ahead, a strong cold front will enter the Gulf of Mexico Sun night, and move across the western Gulf of Mexico on Monday. Strong high pressure will ridge southward behind the front, with a very tight pressure gradient ushering another round of winds to gale force across the Gulf of Tehuantepec. GFS model guidance indicates that these winds may reach strong gale force or storm force. Refer to the latest high seas forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough axis extends from a 1009 mb low near 05N78W to 07N87W to 05N102W, where latest scatterometer data indicates it transitions to the Intertropical Convergence Zone and continues to 07N117W to 10N121W, breaks due to a surface trough extending from 10N125W to 16N121W, then resumes from 10N125W to 09N140W. No significant convection is noted. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please refer to the special features section above for details of a 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 Sun 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 today as the peak swell continues moving southeastward. Divergence aloft southeast of an upper trough along 120W in combination with jet stream energy from the base of the trough northeastward to just S of Baja California and towards central Mexico is supporting a large area of deep layer cloudiness and embedded showers from 10N to 18N between 109W and 119W. A surface trough or a weak low is expected to form along the intertropical convergence zone later today between 120W and 123W, drift westward over the next 48 hours, then dissipate. The gradient between the trough that forms and high pressure over northern waters will increase trade winds sufficiently to build seas to 8-9 ft in mixed NW swell and wind waves. $$ Mundell