000 AXPZ20 KNHC 230235 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 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 0000 UTC surface analysis and satellite imagery through 0300 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec: A Gale Warning will remain in effect for the Gulf of Tehuantepec through Friday morning. Persisting ridge extending southward along the Mexico coastal plains to SE Mexico continues to maintain a relatively tight pressure gradient across the Isthmus of Tehuantepec. This combined with the nocturnal drainage flow will support minimal gale force winds across the Gulf of Tehuantepec tonight into Friday morning. Then, winds will diminish below gale force by early 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, once again with the aid of the nocturnal drainage flow. Winds will further diminish to 20-25 kt Saturday night into Sun morning. Marine guidance suggests that winds will increase to minimal gale force Monday night into Tue morning as a ridge builds again across the western Gulf of Mexico. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 09N84W to 05N93W. The intertropical convergence zone axis continues from 05N93W to 06N105W to 10N122W, then resumes W of a trough at 08N125W to beyond 08N140W. Scattered moderate convection is from 08N to 10N between 110W and 115W. Similar convection is also noted from 07N to 11N between 118W and 121W. A surface trough is within the ITCZ and extends from 13N122W to 09N123W. Scattered showers and isolated thunderstorm are mainly on the E side of the trough to about 120W. ...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 north waters on Saturday. Southerly winds in the 20-30 kt range are expected ahead of the front in the northern Gulf of California with fresh to strong W-NW winds in the wake of the front. The cold front will be moving across northern Baja California and the Gulf of California, including also forecast zones PMZ009, PMZ011, and PMZ013 Saturday and Saturday night. NW winds of 20-25 kt and building seas of 10 to 14 ft in NW 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. Gentle to moderate NW-N winds are noted per scatterometer data over the offshore waters W of Baja California with seas of 8-10 ft in NW swell across much of the area W of 110W. These marine conditions will persist on Friday. On Saturday, expect increasing winds and building seas in association with a cold front reaching the offshore waters. 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 winds are expected thereafter. Locally, these winds will produce seas up to 8 ft. 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... Long period northwest swell continues to impact much of the waters N of 07N west of 110W with seas of 8 to 11 ft. Seas will slightly subside through Friday, but will build back across the northern waters on late Friday as a cold front reaches the northern 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. The most recent scatterometer data indicate an area of fresh to strong trades from roughly 08N to 20N W of 135W, and from 08N TO 17N between 125W and 135W. Seas of 8 to 11 ft, in mixed wind wave and NW swell are noted within the area of the trade winds based on altimeter passes. The high pressure previously located near 31N140W has dissipated ahead of a cold front located N of area. The strong high pressure that follows this front is forecast to move eastward over the next 24 hours, then toward the SE through Saturday approaching the far NW corner of the forecast area. 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, however models differ on just how far south this low will track. $$ GR