000 AXPZ20 KNHC 212141 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Wed Dec 21 2016 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 2100 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec: A gale warning remains in effect for the Gulf of Tehuantepec as a tight pressure gradient continues between a 1026 mb high pressure located over eastern Mexico near 23N99W and relatively lower pressure across southeastern Mexico. In addition, a stationary front remains to the north of the area over the southwest Gulf of Mexico with cooler and drier air continuing to be funneled through the Chivela Pass southward. The most recent scatterometer pass indicated minimal gale force across the Gulf of Tehuantepec, with seas of 14-15 ft. Winds are expected to only gradually diminish through the next couple of days as continuous cold air advection over the western Gulf is likely to reinforce the Tehuantepec event through Friday morning. Gale conditions should likely diminish Friday afternoon as winds veer to the southeast over the western Gulf of Mexico. Northerly winds of 20-30 kt are expected Friday night into Saturday morning. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 08N78W to 06N90W to 05N99W. The ITCZ axis continues from 05N99W to 11N117W, then resumes W of a trough at 10N125W to beyond 07N140W. No significant convection. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of California: The pressure gradient across the area is continuing to weaken and now light to moderate NW winds are noted across the gulf. A cold front approaching from the west will bring an increase in winds across the north waters on Saturday. Southerly winds ahead of a cold front may reach a strong to near gale force breeze in the northern Gulf of California. The cold front will be moving across forecast zones PMZ009, PMZ011, and PMZ013 Saturday and Saturday night. The northwest swell associated with the cold front could produce seas of 9 to 13 ft with the highest of these seas expected to be confined to zone PMZ009, and the northwest section of zone PMZ011 late on Saturday. A 1014 mb surface low at 26N124W is associated with a strong upper-level cutoff low. A trough extend from the low center to 28N120W to 23N117W to 16N118W. A diffluent pattern aloft to the east of the low is helping to induce a swath of scattered moderate isolated strong convection, particularly from 18N to 23N between 114W and 118W. The low will lift to the north and northeast while dissipating tonight. Moisture associated with this system will continue to spread northward across parts of the Baja California Peninsula and the Gulf of California, including also NW Mexico tonight and Friday. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Fresh to strong northeast winds are expected to pulse in and downstream of the Gulf of Papagayo to near 90W during the overnight and early morning hours through Saturday night, with the assistance of the nocturnal drainage flow. Locally, these winds will produce seas up to 8 ft. The fresh northeast swells will merge with a Gulf of Tehuantepec gap wind event to provide a large area of 8 to 12 ft seas downstream of the gap regions. Elsewhere across the region, winds will remain 20 kt or less, with seas below 8 ft through Sunday night. REMAINDER OF THE AREA... The combination of a 1029 mb high centered north of the area near 33N139W and lower pressures in the vicinity of the ITCZ will continue to support a broad area of fresh to strong trades from roughly 08N to 15N west of 133W. Seas of 8 to 11 ft in mixed wind waves and northwest swell cover the majority of the waters north of the ITCZ west of about 115W. The high center is forecast to weaken through Saturday as it moves to the southwest. As a result, the aerial coverage of fresh to strong winds will decrease. Global models suggest that a cold front will sweep through the northern waters Friday night with a brief surge of fresh to strong northerly winds possible behind it north of 28N. A set of large northwest swell with building seas up to about 14 ft along 30N, will arrive behind the front by early Saturday. High pressure behind the front will shift southeastward to near 31N134W by Saturday night. $$ GR