000 AXPZ20 KNHC 110336 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Tue Dec 11 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 0000 UTC surface analysis and satellite imagery through 0230 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 gentle to moderate 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 110W 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 05N77W to 05N83W to 04N91W where it transitions to the ITCZ. The ITCZ then extends along 06N102W to 08N109W to 08N118W. The ITCZ then resumes west of a surface trough from 07N122W and continues past 06N140W. Scattered moderate isolated strong convection is occurring from 02N to 13N west of 124W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...Current strong gale conditions. See above paragraph for more details over next 36 hours. Longer term a new strong gap wind event for the gulf should begin late Fri morning and weaken below gale force on Sat evening. A 1032 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 troughing across the Gulf of California is supporting gentle to moderate northwest winds across the entire Gulf of California. Seas with these winds presently have a maximum of around 3 ft. Model guidance suggests that the pressure gradient will tighten early Thu morning as a strong ridge builds over the state of Idaho. This will lead to fresh to strong winds over almost all of the Gulf of California through Fri morning. Seas of 5 to 9 ft are west of the Baja California Norte due to long-period northwest swell. These seas will 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 near gale force speeds during the overnight and early morning hours over the Gulf of Papagayo tonight and Tue night, then to mainly fresh to strong 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 weakens from 30N126W to 25N135W. Long-period northwest swell generated by winds behind the front propagates out ahead of the front bringing seas in excess of 8 ft to most of the area west of 120W. A tightening pressure gradient resulting from strong high pressure that will build east- southeast behind the front will support fresh to strong northeast trade winds from 08N to 27N west of about 128W through Thu night. Wave model guidance suggests that a rather large area of 8 ft seas associated with mixed swell will stretch from about 02N to 15N between 92W 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 weak surface trough is near 120W from 07N to 14N. Winds are moderate to fresh with seas to 8 ft 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