000 AXPZ20 KNHC 012141 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2135 UTC Mon Jan 1 2018 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 2030 UTC. ..SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Winds will increase to gale force this afternoon over the Gulf of Tehuantepec as strong high pressure building behind a cold front moving across the Gulf of Mexico helps tighten the pressure gradient over the region. This gale event is expected to be strong and long- lasting, with gale force winds persisting for much of the week, and peaking near 45 kt late tonight and again early Thu. Seas will build to 14 ft this evening and peak near 18 ft Tue morning and again on Thu morning. Swell associated with this event will push downstream of the Gulf of Tehuantepec, with seas 8 ft or greater reaching as far south as 05N and west to 108W by midweek. 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 extends from 1012 mb low pressure near 06N79W to 05N90W to 06N100W. The intertropical convergence zone continues from 06N100W to 11N126W, and resumes from 08N131W to beyond 07N140W. Surface trough from 16N128W to 10N132W. Scattered moderate convection was noted from 03N to 07N between 78W and 83W. Scattered moderate to isolated strong convection was noted from 08N to 13N between 115W and 131W. Scattered moderate convection was also observed from 17N to 27N between 118W and 127W, and within 150 nm N of the ITCZ between 131W and 139W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see special features section above for more details about the developing gale force gap wind event in the Gulf of Tehuantepec. Relatively tranquil marine conditions will persist through the week with light to gentle winds prevailing across the forecast waters. Seas in the range of 3 to 5 ft will continue in the offshore waters, while seas in the 1 to 3 ft range will prevail in the Gulf of California. NW swell of 6 to 8 ft will propagate into the waters off Baja California Norte later in the week. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... NE winds will pulse to fresh to strong in the Gulf of Papagayo through the middle of the week. Winds will further increase to near gale force Thursday as high pressure builds north of the area. Light to gentle NE to E winds will prevail elsewhere N of 09N, with gentle to moderate S to SW winds expected S of 09N. Swell up to 8 ft from the Gulf of Tehuantepec gale event may reach the far western waters offshore Guatemala through the week. REMAINDER OF THE AREA... A 1008 mb low pressure is centered near 28N136.5W under a sharp upper trough. An occluded front wraps around the NW semicircle of the low, while a cold front extends from 30N135W to 26N131W to 17N136W. Numerous showers are within 180 nm E of the cold front, N of 26N. Scattered showers and isolated thunderstorms are elsewhere within 90 nm E of the front, and within 150 nm of the center of the low. A recent scatterometer pass this afternoon confirms fresh to strong NW to N winds west of the low, N of 25N over our area E of 140W. Seas are likely 12 to 16 ft under this area of winds, with a broader area of 8 to 11 ft NW swell west of the cold front. The low and associated fronts will weaken as the low lifts NE the next 24 hours, with winds decreasing below 20 kt by Tue afternoon. The NW swell will continue to propagate SE through Tue night, with seas 8 ft or greater reaching as far S as 15N and as far east as 125W Wed morning. The swell will persist over this region well into the latter part of the week. A surface trough that extends from 24N125W to 21N127W is supporting a tight pressure gradient between itself and high pressure to the NE. As measured by a 1738 UTC scatterometer, SE winds of 20 to 25 kt are occurring over the northern portion and just NE of the trough axis. This trough and associated winds will weaken through tonight. Elsewhere mainly gentle to moderate winds and 5 to 7 ft seas will prevail through midweek. The only exception will be NE swell associated with a Gulf of Tehuantepec gale event that will reach as far as 108W by midweek. $$ Latto