000 AXPZ20 KNHC 292204 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 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 1800 UTC surface analysis and satellite imagery through 2145 UTC. ..SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A tight pressure gradient over southeastern Mexico and the Isthmus of Tehuantepec continued to maintain the N to NE gale force winds of the previous days over the central section of the Gulf of Tehuantepec through 15Z this morning. The 1620Z Ascat pass suggested that these winds had diminished slightly to just below gale strength. However, these winds have recently pulsed back up to gale force. Seas in the range of 10 to 14 ft are expected with these winds. The culprit high pressure area over eastern Mexico will slide eastward tonight into Saturday. This will slacken the pressure gradient allowing for the winds to diminish winds below gale force on Saturday morning near 15Z. In addition, winds to the N of the area will veer Saturday which will further diminish winds funneling into the Gulf of Tehuantepec. By Sunday, winds will diminish to 15-20 kt. 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 NW Colombia southwestward to a 1011 mb low at 06N79W and continues to 07N85W to 06N92W, where latest scatterometer data indicates that it transitions to the ITCZ and continues to 06N101W to 08N114W and 09N128W where it is briefly interrupted by a trough that is along a position from 17N128W to 13N129W to 09N130W. The ITCZ then resumes at 09N131W to beyond 09N140W. Scattered moderate convection is noted within 30 nm of the axis between 110W and 115W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: Please refer to the special features section above for details on Gulf of Tehuantepec Gale event. Beyond 48 hours, a strong cold front will push into the Gulf of Mexico late on Sunday. The front will reach the Bay of Campeche Monday, with strong high pressure in its wake expected to induce the next gale force gap wind event over the Gulf of Tehuantepec, possibly as a strong gale. Elsewhere, tranquil marine conditions are expected with light to gentle winds prevailing over the forecast waters. Seas in the range of 3 to 5 ft will continue over the offshore waters, while seas in the 1 to 3 ft range will prevail in the Gulf of California. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... NE winds will pulse to fresh to strong over the Gulf of Papagayo through Wednesday of next week. 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 except for light and variable along and near the surface trough. REMAINDER OF THE AREA... A weakening surface trough is analyzed along a position from 17N128W to 13N129W to 09N130W at 18Z. The strong E winds observed yesterday and through part of the this morning near the northern portion have diminished to fresh winds. Seas of 6 to 8 ft due to mixed NE and NW swell are evident from 16N to 19N between 120W and 130W. These seas will subside to 6 to 7 ft by early Saturday afternoon. Isolated showers are possible within 120 nm either side of the trough from 14N to 17N. Elsewhere, a broad and persistent upper trough is situated N of about 09N and between 109W and 120W. The trough energy in combination with abundant available moisture is resulting scattered showers and isolated thunderstorms from 10N to 19N between 110W and 120W. Scattered showers and patches of rain are seen from 19N to 26N between 110W and 118W mainly due to divergence aloft on the SE sector of an upper level cyclonic circulation near 25N120W. These features will slowly move eastward through Sunday, with upper level moisture, in the form of broken high clouds, continuing to stream eastward from the moisture area towards much of Baja California and central Mexico. Broad ridging dominates the waters north of 20N with gentle to moderate trades farther S, and seas 5 to 7 ft throughout the region. Little change is expected through Sunday. Beyond 48 hours, deepening low pressure will approach the northwest portion of the forecast area Sunday. The pressure gradient between this deepening low and high pressure to the W of the forecast area will bring strong to near gale force winds N of 25N and W of 130W, with the possibility for these winds to reach minimal gale force over this area Monday. $$ Aguirre