000 AXPZ20 KNHC 211904 AAA TWDEP Tropical Weather Discussion...Updated NWS National Hurricane Center Miami FL 1904 UTC Fri Dec 21 2018 Updated Special Features section 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 1830 UTC. ...SPECIAL FEATURES...Updated Gulf of Tehuantepec Gale Warning: A tight pressure gradient resulting from the combination of high pressure building southward over southeastern Mexico in the wake of a Gulf of Mexico cold front with lower pressure south of Mexico has induced gale force winds that are funneling through the Isthmus of Tehuantepec and out across the Gulf of Tehuantepec. The 1630Z Ascat pass clearly revealed northeast 30 to 40 kt winds in a 50 nm wide swath through the midsection of the Gulf. North to northeast winds of 20 to 30 kt were noted elsewhere within 90 nm either side of the gale force winds. An overnight observation from an oil tanker, the Genmar Compatriot, reported surface winds to 40 kt. Most recently, ship with caller ID "C6DQ4" - the Richmond Voyager, reported northeast winds of 40 kt with combined seas of 14 ft near location of 14N96W at 18Z, and ship with caller ID "MAZS6" - the CMA CGM J. Adams, reported north winds of 46 kt with seas of 13 ft near location of 14N95W at 17Z. Visible satellite imagery from throughout the morning and early afternoon shows an arc cloud line propagating away from the Gulf. It is located about 450 to 500 nm SSW of the Gulf. This feature provides a hint that such a gap wind event is already taking place as it marks the leading edge of the surge of these winds. It is expected that the leading edge of the plume of strong gap winds will reach to near 600 nm to the SW of the Gulf of Tehuantepec this evening, with seas around the 11 to 19 ft range within the area of strong winds. The gales will persist through tonight, then diminish on Sat as high pressure north of the area shifts eastward. Please refer to the latest high seas forecast issued under AWIPS/WMO headers HSFEP2/FZNPN03 for more specific marine details. Gulf of Papagayo Gale Warning: High pressure building in behind a cold front that has moved into the northwestern Caribbean is tightening the pressure gradient over Central America. This will allow for northeast winds to soon increased to strong speeds over the Gulf of Papagayo. As the gradient continues to tighten, these winds will further increase to near gale force by early this evening and to gale by late tonight with seas in the 9 to 12 ft range. These winds are then forecast to diminish to below gale force by early Sat afternoon as the gradient slackens. Seas are forecast to max out to around 14 ft between 60 and 150 nm downstream of the Gulf Sat morning into Sat afternoon, with little change on Sun as the northeast winds remain at near gale force. Extended model outlook indicates that strong gap winds will continue flowing over the Gulf of Papagayo through the middle of next week. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough extends from northwestern Colombia to 07N78W to 05N94W, where latest scatterometer data indicated that it transitions to the ITCZ. The ITCZ extends from 05N94W to 06N110W to 06N125W to 05N136W to beyond the area at 07N140W. Scattered moderate convection is north of the ITCZ within 30 nm of a line from 10N114W to 10N120W and also within 30 nm of the ITCZ between 103W and 110W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the Special Features Section above for information on the ongoing strong gale force gap wind over the Gulf of Tehuantepec. Subsiding long period NW swell will continue to propagate across the region. Seas of 8 ft or greater cover much of the open ocean waters in the discussion area. Seas everywhere outside the Gulf of Tehunatepec will continue to subside through early Sat. The next round of large swell is forecast by Wave model guidance to reach the offshore waters of Baja California Norte by early on Mon and the remainder of the Baja California Peninsula offshore waters by early on Tue. The guidance depicts seas to build to the range of 10 to 14 ft offshore Baja California Norte on Tue. Elsewhere, weakening high pressure over the Great Basin supports fresh northwest winds in the central Gulf of California, which will become light and variable by tonight. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Please the Special Features Section for more on the upcoming gale force gap wind event over the Gulf of Papagayo. Strong north winds will begin to over the Gulf of Panama beginning late tonight and are expected to last through Sun night, with seas starting at less than 8 ft but building to 8 ft by early on Sun. Elsewhere, gentle to moderate winds will persist, with seas in the 4 to 7 ft range. REMAINDER OF THE AREA... A cold front is analyzed from near 32N129W to 28N135W where it becomes stationary to beyond the area at 25N140W. The front is located over a large area of 9 to 10 ft seas due to a northwest swell that is presently decaying. The front will slowly become diffuse through this evening as high pressure behind builds southeast and south. The pressure gradient between the high pressure and lower pressure present in the tropics has initiated an area of strong northeast trades from 09N to 14N west of 136W along with seas in the range of 11 to 14 ft due to the northwest swell combining with the northeast trades. This area of trades will change little through late tonight, then expand north and east Sat through early next week. The seas of 11 to 14 ft will shift west of the area during this time as the northwest swell decays allowing for the seas associated with these trades to lower a little. Northwest swell propagating through the discussion area is decaying making seas north of 20N and W of 120W to lower through Sat. An area of mixed swell will develop south of about 16N between 100W and 112W by late Sat as lingering NW swell mixes with shorter period northeast swell from the Tehuantepec and Papagayo gap wind events. $$ Aguirre