000 AXPZ20 KNHC 062131 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Wed Dec 6 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 2130 UTC. ...SPECIAL FEATURES... Gulf of California Gale... An extensive area of strong high pressure from the U.S. Great Basin and northern Rockies will continue to support fresh to occasionally strong NW winds over the northern Gulf through late tonight. The gradient will tighten further into Thursday morning as reinforcing high pressure follows in behind a cold front moving southward along the front range of the Rockies. This will allow for the fresh to occasionally strong winds to increase to Gale force, 30-35 kt winds over the gulf N of 27N by Thursday morning. NW winds of 20-30 kt are expected elsewhere across the gulf N of 26N. Latest model guidance impressively shows that these gale wind conditions will persist through late Thursday night as they surge southward to 26N, with winds veering to the N-NE N of 26N. Also of significance is that waveheight model guidance indicates that seas will build to maximums of 10 and 11 ft over the northern gulf waters by early Thursday afternoon and to include the central portion of the gulf by late Thursday night. Winds and seas will then diminish into Sunday as the aforementioned high pressure N of the area weakens. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The Monsoon Trough axis extends from 10N85W to 07N90W to 07N100W, where it transitions to the Intertropical Convergence Zone (ITCZ) and continues to 08N105W to 09N120W to 11N128W where it ends. It then resumes at 11N135W southwestward to beyond the area at 09N140W. Scattered moderate to isolated strong convection is within 60 nm of the axis between 110W-116W. Scattered moderate convection is within 60 nm N of the axis between 116W-119W, and also within 30 nm of 08N104W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: N to NE winds of 20-25 kt are funneling into the gulf with maximum wave heights up to 9 ft. These winds will increase to 20-30 kt late tonight as a strong cold front drops southward over the western Gulf of Mexico waters and southeastern Mexico. The tight pressure gradient over southeastern Mexico will keep this wind range through Friday, with maximum wave heights building to around 11 ft per latest TAFB NWPS and MWW3 wave guidance. Looking ahead, strong high pressure will press southward in the wake of the strong Gulf of Mexico cold front will favor the development of a persistent strong gale event for the Gulf of Tehuantepec beginning on Friday night and to continue through the upcoming weekend. 12Z 925 mb and 30-meter wind guidance from the GFS suggest and the same 18Z guidance from the NAM suggests winds will be in the 50-60 kt at those levels. This increases the probability of the forecast strong gale force winds will be upgraded to a storm warning in future forecast updates. Elsewhere off the Pacific coast of Mexico, weak high pressure is maintaining gentle to moderate breezes across the region. High pressure building to the N of the area will result in strong gap winds pushing across low lying area of Baja California Norte and into adjacent waters Thu. A larger plume of strong NE winds will push off the coast of Baja California Sur north of Cabo San Lazaro beginning on Thursday night and through Friday before diminishing Friday night and Saturday. Wave heights associated with these winds are expected to build to a maximum of 10 or 11 ft reaching from near shore to beyond 250 nm offshore. Although not explicitly forecast in the High Seas, the potential exists for locally gale force winds through the passes of Baja California into the adjacent Pacific coastal areas. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: NE winds of 20-25 kt through the Gulf of Papagayo will diminish to 15-20 kt this afternoon, then pulse back up to 20-25 kt tonight and diminish back to 15-20 kt Thursday morning. Elsewhere, light to gentle N to NE winds are expected N of the monsoon trough, and mainly gentle to moderate S to SW winds are expected to the S of the monsoon trough. Seas are in the 5 to 7 ft range in SW swell this evening to the S of the monsoon trough, and will subside to 4-6 ft through mid week. Large NW swell with wave heights of 8-10 ft from the upcoming Tehuantepec gap wind event will spread across the offshore waters of Guatemala late this week and over the weekend. REMAINDER OF THE AREA... The pressure gradient is tightening over NW waters as a cold front has entered the area along 30N139W to 27N140W. This front will result in fresh to strong SE to S winds N of 28N and W of 135W with wave heights in the range of 9-11 ft. The front is forecast to weaken as it moves through the far NW corner of the area later tonight and Thu, at which time the area of fresh to strong SE to S winds will move N of the area. A second cold front approaches the far NW waters by Friday. A very large area of NW swell that expected to encompass a large chunk of the W and central sections of the area to the W of a line from 30N129W to 20N125W to 07N140W by Friday with induced wave heights in the range of 8-11 ft. The highest of this range will be located in the far NW portion of the area. A surface trough along 128W/129W from 10N-18N is drifting westward. A tight pressure gradient will develop N and NE of this trough between it and strong high that shifts eastward over the central and NE waters. This will lead to a brief period of NE-E 20-25 kt winds from 18N-22N between 127W-131W Thursday evening with induced wave heights of 8-10 ft. By Friday this area of seas merges with a larger area of seas described above as the trough weakens. Elsewhere, long period NW swell producing seas of 8 ft to the S of 10N between 100W-115W and also S of 02N between 115W-130W will gradually diminish in coverage through late Thursday night, with seas subsiding to less than 8 ft and winds to 20 kt or less early on Friday. $$ Cobb