000 AXPZ20 KNHC 202205 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Tue Dec 20 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 is in effect for the Gulf of Tehuantepec. A strong Gulf of Tehuantepec gap wind event commenced Sunday night due to a cold front that crossed the Gulf of Mexico. Cooler, drier air behind the front has been moving across the isthmus of Tehuantepec into the Gulf of Tehuantepec. At 1800 UTC, ship C6BZ9 reported NNE 35 kt wind and 15 ft significant wave height a couple hundred nm south of Salina Cruz, while ship D5KA4 observed NE 25 kt wind and 15 ft significant wave height about 300 nm south of Salina Cruz. Additionally, an earlier 1200 UTC TOPEX altimeter pass showed peak wave heights of 14-16 ft. The event is gradually weakening and peak winds currently are around 40 kt with largest wave heights of around 18 ft. Winds should very gradually diminish as the next cold front moving across the Gulf of Mexico is likely to reinforce the Tehuantepec event on Thursday and Friday. Gale conditions should likely diminish for good by late Saturday. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 05N77W to 06N91W. The Intertropical Convergence Zone axis extends from 06N91W to 10N109W, then resumes at 10N124W to beyond 07N140W. Scattered moderate isolated strong convection is within 120 nm S of ITCZ axis between 124W and 136W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of California: At 2000 UTC, ship KAQP reported 30 kt NW winds in the central Gulf of California. Additionally, the 1654 and 1740 UTC scatterometer passes indicated NW 25 kt winds in about the same location. No wave height measurements were available, unfortunately. These winds are the result of a strong pressure gradient between a 1040 mb high over the Four Corners area and a trough along the southern Gulf of California. These conditions should diminish to below 25 kt by Wednesday morning as the high weakens and shifts eastward, leaving areas of 20 to 25 kt winds across the Gulf. A strong upper-level cutoff low has induced a surface trough from 19N119W to 11N123W. Scattered moderate and isolated strong convection exists within 120 nm east of the trough from 10N to 16N. Additionally, numerous moderate and scattered strong convection exists from 16N to 22N between 111W and 117W. The aforementioned scatterometer passes suggested that there were gale force winds associated with this system. However, these are likely incorrect, due to rain contamination of the scatterometer measurements. Nonetheless, E to SE winds of 20 to 30 kt are likely occurring on the east side of the trough with seas of 8 to 10 ft. These conditions should diminish early on Thursday. NW swell will continue to impact the offshore waters W of Baja. Seas associated with the trough/low are forecast to merge with additional pulses of NW swell arriving Wednesday night through Friday. By Thursday morning, expect seas of 8-10 ft N of 20N w of 115W. A cold front will approach Baja California norte by the end of the week, moving across the area late Saturday. A brief surge of 20 to 25 kt winds both ahead of and behind the front is possible, with sea heights of 10 to 16 ft propagating across the NE forecast waters...including forecast zones PMZ009, PMZ011, and part of PMZ013 during the upcoming weekend. 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 morning, with the assistance of the nocturnal drainage flow. Locally, these winds will produce up to 8 to 9 ft seas. The fresh northeast swells will merge with the Gulf of Tehuantepec gap wind event to provide a large area of 8 to 12 ft seas downstream of the gap regions. Gulf of Panama: Fresh northerly winds and seas to near 6 ft are noted across this Gulf to about 06N80W. These marine conditions will persist tonight, then mainly moderate northerly winds are expected on subsequent nights. Elsewhere across the region, winds will remain 20 kt or less, with seas below 8 ft through Saturday night. REMAINDER OF THE AREA... A 1033 mb high centered north of the area near 33N136W extends a ridge across the waters north of the ITCZ W of 120W. This ridge combined with the aforementioned trough continues to support a broad area of fresh to strong trades from roughly 08N to 26N west of 120W. Based on altimeter data, seas of 8 to 12 ft in mixed wind waves and NW swell, cover the majority of the waters north of the ITCZ west of 120W. The high center is forecast to move westward over the next 24 hours while slightly weakening. As a result, the aerial coverage of fresh to strong winds will decrease by Wednesday and remain limited through Saturday. A cold front will drop south into the northern waters Friday night with a brief surge of 20 to 25 kt northerly winds possible behind it north of 28N. Large northwest swells, building seas up to 16 ft along 30N, will arrive behind the front on Saturday. $$ GR/CWL