000 AXPZ20 KNHC 050346 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Fri Jan 5 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 0000 UTC surface analysis and satellite imagery through 0300 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: The existence of a well entrenched very tight pressure over southeastern Mexico and lower pressures to the S of the Gulf of Tehuantepec region continues to maintain strong gale force N to NE winds over the Gulf of Tehuantepec. These winds peaked to 45 kt early on Thursday. Gale force winds are expected to continue into the first half of the weekend, before diminishing below gale force Sunday. Swell generated from the persistent gale force winds will propagate downstream of the Gulf of Tehuantepec, with seas 8 ft or greater reaching as far S as 05N and west to 110W by Friday afternoon. Yet another gale wind force gap wind event is forecast by the global models and regional NAM model by Monday evening. Please refer to the latest high seas forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more details. A low pressure system, induced by a rather potent mid/upper level low embedded within a large mid/upper trough, is expected to develop over the northwestern waters on Friday. Presently, a surface trough extends from 25N126W to 18N134W to near 12N137W. The trough is underneath the eastern periphery of the mid/upper trough. Very deep moisture observed here along with an amplified diffluent flow aloft is sustaining a large batch of rain along with embedded scattered showers and isolated thunderstorms as observed on satellite imagery from 16N to 25N between 127W and 132W. The pressure gradient expected to evolve between the forecast deepening low pressure system and high pressure over the far western portion of the area will induce strong to minimal gale force winds to the W of the low, and also to the W of the trough forecast to extend from the low northward to 30N129W beginning Friday night. The low is forecast to weaken as it slowly moves westward over the NW portion of the area late Sunday. The associated gale force winds are expected to continue over the NW waters in the NW and W quadrants of the low through late Saturday night, with resultant seas of 12-16 ft subsiding to 10-14 ft on Sunday. Although there are differences in the model guidance with respect to actual position and pressure of the low through early on Sunday, the guidance is in very good agreement that the low will be shunted to ENE by a frontal system on Monday while at the same time being absorbed by it. Please 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 0778W to 07N87W to 07N96W to 06N107W, where latest scatterometer data indicated the ITCZ axis then begins and continues to 08N119W to 09N130W to 09N140W. Scattered moderate convection is seen within 30 nm N of the axis between 124W and 128W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see Special Features section above for more details about the ongoing gale force wind event in the Gulf of Tehuantepec. Relatively tranquil marine conditions will persist through Friday, with light to gentle winds prevailing across the forecast waters under the influence of a 1019 mb high pressure located near 27N119W. Seas in the range of 3-5 ft will continue over most of the offshore waters through today, while seas in the 1-3 ft range will prevail in the Gulf of California, with the exception of 3-4 ft across the central waters through early Friday. NW swell will propagate into the region, with seas building in the range of 5-7 ft through the waters offshore Baja California Norte this evening. The high pressure will reach a position to near 30N121W by early Friday morning. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: NE winds will pulse to near gale force during the overnight and early morning hours starting tonight as high pressure builds north of the area tightening the pressure gradient. Light to gentle NE-E winds will prevail elsewhere to the N of 09N, with gentle to moderate S to SW winds expected S of 09N. REMAINDER OF THE AREA... Please see Special Features section above for details about forecast gale center over the NW waters. The pressure gradient between this low and high pressure to the W of the forecast waters will also support a large area of fresh to strong northerly winds roughly N of 20N W of 130W with seas of 8-12 ft in NW swell. Fresh to strong southerly winds are also expected N of 20N E of low center to about 124W with similar sea heights. Currently, seas of 8 ft or greater are present NW of a line from 30N124W to 17N128W to 13N140W, with seas peaking near 11 ft over the far NW waters as highlighted by the latest altimeter data. The swell will continue to propagate southeastward, with seas 8 ft or greater covering much of the water north of 15N and W of 124W by Friday night. A cold front is expected to move into into the NW waters next Monday, followed by increasing winds and building seas. $$ Aguirre