000 AXPZ20 KNHC 102206 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Mon Dec 10 2018 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 2145 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: High pressure is ridging southward along the eastern slopes of the Sierra Madre Oriental mountains of Mexico. The large pressure difference between the high pressure and lower pressure south of Mexico will maintain strong gale force winds over the Gulf until early Wed morning. Seas in the gale warning area are forecast to build to 20 ft by late tonight. The strong gale force winds will continue through Tue, then diminish to minimal gale force Tue night. Winds will then rapidly decrease and become light by Wed evening as strong high pressure over the Gulf of Mexico weakens and shifts E. Swell from this event is forecast to propagate south and southwest well away from the Gulf of Tehuantepec region, with the leading edge of the 8 ft seas expected to reach to 111W and 02N late Tue night. This area of 8 ft seas will merge with a larger area of 8 ft seas approaching from the northwest. Please refer to the Eastern Pacific High Seas Forecast under AWIPS/WMO headers HSFEP2/FZPN03 KNHC for more specific marine details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from a 1010 mb low in western Colombia near 05N76W to 04N83W to 04N94W where it transitions to the ITCZ. The ITCZ then extends along 06N103W to 07N111W then resumes west of a surafce trough near 08N119W and continues past 07N140W. Scattered moderate convection is occurring within from 04N to 13N west of 124W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...Gale warning in advance. See above paragraph for more details over next 42 hours. Longer term a new gap wind event for the gulf should begin early Fri and should reach strong gale on Fri and weaken below gale force on Sat afternoon. A 1033 mb high pressure system located NW of the area extends a ridge southeast to the Revillagigedo Islands. The pressure gradient between the high pressure and enhanced troughing across the Gulf of California is supporting moderate northwest winds across the entire Gulf of California. Seas with these winds presently have a maximum of around 5 ft. Beyond 42 hours, model guidance suggests that the pressure gradient will further tighten leading to fresh winds over almost all of the Gulf of California and within 60 nm of the Baja Peninsula on Thu and Thu night. Seas of 5 to 7 ft prevail west of the Baja California Peninsula, however, wave model guidance indicates that a new set of long- period northwest swell producing much larger seas, in the range of 8 to 10 ft, will reach the waters off the northern Baja California coast and near Guadalupe Island beginning tonight, then spread east to cover most of the waters off the entire Baja California peninsula and the Revillagigedo Islands through Tue night, before subsiding below 8 ft through Wed evening. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo...Winds will pulse to strong speeds during the overnight and early morning hours over the Gulf of Papagayo tonight and Tue night, then to mainly fresh speeds Wed night as high pressure over the Gulf of Mexico builds southeastward toward the NW Caribbean Sea and Central America. Elsewhere, gentle to moderate winds will persist on either side of a weakening monsoon trough and seas in the range of 4 to 6 ft. REMAINDER OF THE AREA... A cold front is analyzed from 30N128W to 26N138W at 18 UTC. Long- period northwest swell generated by winds behind the front propagates out ahead of the front. This will bring seas in excess of 8 ft to most of the area west of 120W through early Tue. This will reinforce the decaying northwest swell lingering south of 20N which are mixed with shorter period trade wind swell. A tightening pressure gradient resulting from strong high pressure that will build east-southeast behind the front will support mainly fresh northeast trade winds from 10N to 20N west of about 125W through Wed, with fresh to strong winds west of 133W. Wave model guidance suggests that a rather large area of 8 ft seas associated with mixed swell will stretch from about 03N to 13N between 94W and 110W as a result of long-period northwest swell mixing with shorter period northeast swell that propagate downstream from the Gulf of Tehuantepec and to a smaller extent those induced by the Gulf of Papagayo strong nocturnal pulsing northeast winds. This area of swell will begin to merge with an even larger area of seas associated with northwest swell which will cover almost all of the forecast area west of around 92W by Wed. A well-defined surface trough is near 117W from 05N to 12N. Winds are fresh associated with the trough. The trough is positioned to the east of a very well pronounced upper-level trough as seen in water vapor. The upper-level trough will amplify southward during the next couple of days, while at the same time the surface trough gradually loses its identity as it continues in a westward motion. $$ Ramos