000 AXPZ20 KNHC 052203 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Wed Dec 05 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 2100 UTC. ...SPECIAL FEATURE... Gulf of Tehuantepec Gale Warning: Minimal northerly gale force winds will persist across and downstream of the Gulf through late tonight, and reach as far S as 14.5N96W this afternoon. Associated seas will build to a peak around 13 ft downstream near 14.5N95.5W this afternoon through this evening before winds and seas gradually begin to diminish to below gale force by around sunrise Thu morning. Winds will further diminish to 20 kt or less by Fri afternoon as the supporting high pressure across the Gulf of Mexico shifts E into the Atlantic. The next gap event is expected to begin on Sun morning and quickly increase to strong gale conditions by Sun evening and persisting through Mon night. .INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 07N78W along the Panama-Columbia border westward to 09N108W. The monsoon trough then resumes at 09N113W and extends to 09N131W. the ITCZ begins at that point and extends westward to 09N140W. Isolated moderate convection is observed within 180 nm south of the monsoon trough between 85W and 95W. Scattered moderate convection exists within 120 nm of the monsoon trough between 118W and 127W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...See special features paragraph above. Weak high pressure is centered offshore of Baja California Sur this morning near 21N117W, and is yielding light and variable wind flow E of 117W, and gentle NWly wind flow through the length of the Gulf of California. Seas are generally 2 to 4 ft in NW swell across the offshore Baja waters this afternoon and evening. Southerly flow will develop W of Baja Norte late this afternoon and evening ahead of a cold front approaching the area from the NW today, with fresh S to SW winds spreading into the northern offshore zones tonight through Thu ahead of the front. This front will reach from the coast near the California-Baja California border to 30N117W to 20N128W on Thu morning, then across Baja California Norte Thu night, reaching across the northern Gulf of California near 30N113W to 25N116W to 20N122W by Fri morning, and all the way to southern portions by Sat morning. SW winds will diminish ahead of the front late Thu through Fri, but long-period NW swell will begin to move into the offshore waters early Fri morning, producing building seas of 6-8 ft Fri morning, and 7-9 ft by Sat morning. Satellite imagery this afternoon shows dense overcast high clouds streaming SW to NE across central Baja California. This is an indication of a southern upper level jetstream moving into the region ahead of an upper trough. As the cold front approaches Baja California Norte Thu morning, this jetstream will produce unstable conditions aloft, and help to transport low and middle level moisture into the Baja Peninsula and spread NE into NW Mexico. Periods of moderate to briefly heavy rain will affect the southern half of the Baja Peninsula and the western slopes of the Sierra Madre Occidentales Thu through Fri evening as this weather system moves SE into the region. Gulf of California: A pre-frontal trough will pass E through the the northern gulf waters tonight and Thu, followed by the associated cold front late Thu night into Fri, with fresh northerly flow forecast briefly behind both the trough and the front. Gentle to locally moderate northerly flow expected across the entire gulf waters on Sat. Then the pressure gradient will tighten with fresh to locally strong NW flow expected across the southern and central gulf waters on Sat night and Sun. The next round of long-period NW swell, in the form of 7 to 9 ft seas, will reach 32N120W on Mon and propagate S across the waters W of the entire Baja Peninsula on Tue. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... A thin plume of volcanic ash originating interior Guatemala is observed on satellite imagery spreading southwest across the Pacific coast of Guatemala and Mexico between 13.5N and 14.5N, but is not likely to be reaching the surface. Gulf of Papagayo...Nocturnal pulses of fresh to locally strong NE winds, and 6 to 9 ft seas, are expected through Fri night across and downstream of the Gulf, and will extends as far W as 09.5N91W on Thu, and create a broad band of fresh to strong winds nearly 200 nm wide. Elsewhere: The monsoon trough will meander between 08N and 10N this week with light to gentle variable flow, and 3 to 5 ft seas, forecast N of the monsoon trough, and moderate southwesterly monsoonal flow, and 4 to 6 ft seas, forecast S of the monsoon trough. REMAINDER OF THE AREA... A surface low supporting the cold front approaching Baja California will shift SE into the area to near the California- Baja California border Thu evening, and then move E along 32N passing E of 120W on Fri night. This will drag the aforementioned cold front eastward across the subtropical waters. Large 8 to 13 ft seas, in long-period NW swell, is forecast to propagate E across the area, with the leading edge of 8 ft or greater seas reaching from 32N120W to 10N140W on Thu, and from the southern tip of the Baja Peninsula to the equator at 130W on Fri night. Another cold front will reach 32N137W on Fri accompanied by a moderate wind shift. A stronger cold front will reach 32N140W on Sat evening accompanied by a fresh wind shift and large post- frontal NW swell. $$ Stripling/Landsea