000 AXPZ20 KNHC 301605 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Wed Dec 30 2020 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 1545 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 09N79W to 09N86W to 06N95W and to 05N109W, where overnight scatterometer data indicates that it transitions to the ITCZ and continues to 07N120W to 06N130W and to beyond the area at 06N140W. Scattered moderate to isolated strong convection is within 180 nm north of the ITCZ between 125W-130W and also within 120 NM north of the ITCZ between 130W-135w. Scattered moderate convection is within 60 nm south of the ITCZ between 125W-128W and within 30 nm south of the ITCZ between 130W-135W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... The gradient associated with high pressure ridging over this part of the area is allowing for fresh to strong northwest winds to exist over these waters. Fresh to strong northwest winds have materialized over the Gulf of California. Wave heights are in the range of 9-11 ft over the offshore waters and less than 8 ft in the Gulf of California. The 9-11 ft wave heights are embedded within a large set of northwest swell that has its leading edge of wave heights to 8 ft reaching as far as the Revillagigedo Islands. The main weather driver is a mid to upper level trough swinging southeastward along a water vapor interpreted position from northeastern Arizona, southwestward to over northwestern Mexico and to offshore Baja California Sur near 20N118W. This feature will move eastward through this morning, supporting lower pressure over the southern Plains and north central Mexico. Ridging will build behind this trough over the Great Basin and eastern Pacific, tightening the pressure gradient and allowing for the present northwest winds over the Gulf of California to increase to near gale strength over the central and southern Gulf of California today and tonight along with wave heights building to or near 9 ft. Northwest winds will also increase off Baja California Sur by late Wed. The aforementioned northwest swell will continue to propagate southward, with heights to 8 ft reaching as far south as Cabo Corrientes by Thu night. The fresh to strong northwest winds will diminish Thu as the high pressure north of the area shifts east. But another, weaker deep-layer trough moving through the region will support strong NW winds in the northern Gulf of California Thu night, and off Baja California Norte with a reinforcing set of northwest swell raising wave heights to 12 ft. Winds and seas diminish Fri into Sat. Wave heights exceeding 8 ft will continue off Baja California due to a northwest swell. Looking ahead, another set of northwest swell is forecast into the area, with wave heights building significantly to the range of 12-14 ft in the waters north of Cabo San Lazaro late Sat through Sun night. Farther south, overnight scatterometer satellite data from part of the Gulf of Tehuantepec and nearby land-based observations indicated that winds there have diminished to gentle to moderate speeds over the Gulf of Tehuantepec. Residual swell from the earlier gap winds is subsiding, and wave heights are likely in the range of 5-7 ft primarily due to long-period southwest swell. Looking ahead, the next gale force gap wind event in the Gulf of Tehuantepec is expected by late Sat through Sun night as a cold front moves through the Gulf of Mexico and high pressure in its wake ridges southward across eastern Mexico. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and WITHIN 750 NM OF ECUADOR... Fresh to locally strong northeast gap winds across the Gulf of Papagayo region will diminish to mainly fresh speeds this afternoon. Wave heights will subside to about a maximum of 5 ft by this afternoon, with little change through the rest of the week. The next round of fresh to fresh gap winds is possible by late Sat into early Sun. Elsewhere, gentle to moderate winds along with slight to moderate wave heights due to a southwest swell will remain over the Central American and equatorial waters through Sun night. REMAINDER OF THE AREA... A 1032 mb high center is analyzed just north of the area at 33N136W, with a ridge stretching southeastward to the Revillagigedo Islands. Overnight ASCAT data and a couple of ship observations indicated that the pressure gradient resulting from the interaction between the ridge and the ITCZ to the south is resulting in fresh northeast to east trades over the deep tropics west of about 130W, with a pocket of fresh to strong trades present from 15N to 20N west of 130W. The trades will expand eastward to near 120W tonight as the ridge strengthens. A recent altimeter pass showed wave heights in the range of 8-11 ft north of about 07N and west of 110W likely due to the combination of northeast wind waves with long-period northwest swell propagating through this part of the discussion area. The ridge will weaken Thu and shifts east ahead of an approaching cold front, allowing for northeast trade winds o diminish back to moderate to fresh conditions. Maximum wave heights will be about 10 or 11 ft and wave heights of 8 ft or greater will remain west of 110W and north of 04N through Fri. The cold front is forecast to become stationary near 30N140W by late Fri, but a reinforcing set of northwest will accompany the front with wave heights 12 ft or greater covering the waters northwest of a line from Baja California Norte to 12N140W by Sat night through Sun. $$ Aguirre