000 AXPZ20 KNHC 120251 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Tue Dec 12 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 0000 UTC surface analysis and satellite imagery through 0230 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Storm Warning: A very tight pressure gradient is sustained across the Isthmus of Tehuantepec by 1028 mb high pressure centered just west of Tampico Mexico. This tight pressure gradient will maintain strong gale force winds in the range of 30-40 kt over the Gulf of Tehuantepec until early on Tuesday, then diminish to minimal gale force by early on Wednesday. Seas are in the 12-18 ft range with these strong gale force, and will subside to 10-15 ft early in Tuesday and remain near those values through Wednesday. Fresh to strong NE-E winds extend downstream from the gulf to near 10N and 100W, where seas are in the 9-14 ft range primarily due to a NE swell. A large area of NE-E 15-20 kt winds is confined from 02N-15N between 90W- 110W, with seas of 8-12 ft in mixed NE and SW swell. This area is forecast to gradually shrink in coverage through Thursday. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The Monsoon Trough axis extends from a 1009 mb low over NW Colombia to 09N79W to low pressure near 07N86W 1010 mb to 04N95W where latest scatterometer data indicated the ITCZ begins and continues to 08N108W to 10N119W where it is bisected by a trough that is along a position from 20N114W to 14N119W to 10N125W. The ITCZ resumes at 10N129W to beyond the area at 08N140W. No significant convection is noted. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: Please see Special Features section above for details on the ongoing gale event. A weaker pressure gradient than the past few days is presently over the SW U.S. This is maintaining generally gentle to moderate NW winds across the gulf. The gradient will between very strong high pressure that builds southward over the western U.S. and the thermal troughing will support the NW winds to increase over the northern portion of the gulf beginning on Tuesday, with winds there reaching the fresh category. These winds then increase further to the strong category on Wednesday and through Wednesday evening. Mainly moderate NW-N winds over the offshore Pacific waters along with seas of 4-6 ft will change little through Thursday. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR...Corrected Gulf of Papagayo: The tight pressure gradient over southeastern Mexico has slackened just enough to allow for the recent gale force NE winds that were present across the Gulf of Papagayo to diminish to strong to near gale force winds this morning. N-NE winds of 20-25 kt are elsewhere N of 08N between 85W-86W. Model guidance indicates that these winds will change little through Wednesday with seas in the range of 8-10 ft. These seas will propagate to the SW away from the fetch area, and reach to near 08N and 98W on Thursday. REMAINDER OF THE AREA... A dissipating stationary front is across the NW corner of the area from 30N136W to 28N140W. The main issue over the western half of the area is the long period NW swell that is located to the W of a line from 32N128W to 21N132W to 14N128W to 09N140W. The swell is inducing seas of 8-12 ft, with the highest of these seas N of 22N. The swell will gradually decay through Thursday, at which time it is forecast to be the W of a line from 32N134W to 23N140W along with seas of 8-11 ft. The pressure difference between a trough roughly along a position from 20N114W to 14N119W to 10N125W and the high pressure over the northern and central waters is forecast to result in strong NE to E winds beginning late tonight from 13N-18N and between 128W-137W along with seas of about 8-10 ft. This area of strong winds will diminish on Tuesday, with winds diminishing to 15-20 kt. $$ Aguirre