000 AXPZ20 KNHC 221557 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Thu Dec 22 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 1200 UTC surface analysis and satellite imagery through 1530 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: High pressure ridging stretching southward along Sierra Madre Oriental mountains of Mexico combined with lower pressures south of the Tehuantepec area continues to result in a tight pressure gradient. This gradient assisted by nocturnal drainage flow is maintaining northerly gale force winds across the Tehuantepec waters. Model guidance indicates that the ridging will gradually slacken through Friday morning and into early Friday afternoon at which the gale force winds are forecast to drop to just below gale force. Expect fresh to near gale force northerly winds to then continue through Saturday morning, diminishing Saturday afternoon. Beyond the forecast period, northerly winds will then pulse to fresh to strong the next couple of nights this weekend, with another gale force wind event possible by Tuesday of next week. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 09N83W to 05N93W to 05N97W. The intertropical convergence zone axis extends from 05N97W to 07N106W to 08N118W, where it is disrupted by a surface trough that extends from 15N120W TO 08N122W. The ITCZ resumes from 08N124W to 08N133W to beyond 08N140W. Scattered moderate convection is within 120 nm west of the trough from 13N to 14N, and within 30 nm of the axis between 130W and 133W and between 134W and 139W. Scattered moderate convection is north of the ITCZ within 30 nm of 13N112W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of California: Mainly light to moderate southerly flow will prevail across the northern half of the gulf, with light to moderate northerly flow across the southern half through Friday. A cold front approaching from the west will bring an increase in winds across the northern gulf by early Saturday with 20 to 30 kt winds possible. The cold front will be moving across northern Baja California and the Gulf of California, also including forecast zones PMZ009, PMZ011, and PMZ013 Saturday and Saturday night. Northwest winds of 20 to 25 kt and building seas of 9 to 13 ft in northwest swell are expected in the wake of the front. The highest of these seas are forecast to be confined to zone PMZ009, and the northwest section of zone PMZ011 late on Saturday. A weak 1013 mb surface low at 32N118W is collocated with a strong upper-level cutoff low. A trough extends from the low center to 26N121W and to 21N123W, however the previous convective activity has diminished during the morning. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Fresh to strong northeast winds will continue to pulse during the overnight and early morning hours with the assistance of nocturnal drainage flow through Friday morning, then moderate to fresh thereafter. Locally, these winds will produce seas up to 8 ft. The fresh northeast swell will continue to merge with a Gulf of Tehuantepec gap wind event to provide a large area of 8 to 11 ft seas downstream of the gap regions through this afternoon. Elsewhere across the region, winds will remain 20 kt or less, with seas below 8 ft through Saturday. Moderate Northerly winds are expected across the Gulf of Panama during the overnight and early morning hours. REMAINDER OF THE AREA... The combination of a 1028 mb high centered just north of the area near 32N140W and lower pressures in the vicinity of the ITCZ will continue to support a belt of fresh to strong trades from roughly 08N to 18N west of 122W. Seas of 8 to 11 ft in mixed wind waves and northwest swell within the area of the trade winds as was noted by overnight altimeter passes. 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. Long period northwest swell continues to impact much of the waters west of 115W with seas of 8 to 11 ft. Seas will slightly subside through Friday, but will build back across the northern waters on late Friday a cold front reaches the forecast area Friday night. Fresh to strong northerly winds and a new set of large northwest swell, with building seas up to about 14 ft along 30N, will follow the front. High pressure behind the front will shift southeastward to near 28N139W by Sunday morning. As this high pressure builds in, the aerial extent of the trades will increase again. The next cold front will drop into the northern waters Sunday night, while a parent surface low manages to rotate into the area by Monday night. $$ Aguirre