000 AXPZ20 KNHC 070942 CCA TWDEP CORRECTED MONSOON TROUGH AND ITCZ CONVECTION Tropical Weather Discussion NWS National Hurricane Center Miami FL 837 UTC Thu Dec 7 2017 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 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Gulf of California Gale... 1046 mb high pressure is centered north of the area over the Great Basin and Northern Rockies, along with 1029 mb high pressure over west Texas. A tight gradient between these high pressure systems and troughing over the southwest United States, Baja California and northwest Mexico is supporting strong winds down the Colorado River Valley this morning. Fresh to strong winds increase to minimal gale force over the northern Gulf of California starting by late morning to early afternoon, with seas building to 11 ft. Gale force winds will also spread through the central Gulf by late Thu as strong NW winds enter the southern Gulf, with seas building 8 to 10 ft. The strong high pressure over west Texas will shift southward into north central Mexico late today and tonight, while low pressure remains over the entrance to the Gulf of California. This will allow the strong to gale force winds to veer from the NW to the NE and E. This will limit the fetch and allow seas to subside. The winds will diminish Fri into Sat as the low pressure weakens. Fresh to strong NW winds will persist over the northern Gulf into Sun then diminish below 20 kt. Gulf of Tehuantepec Gale... Gulf of Tehuantepec: N to NE winds of 20-30 kt are funneling into the Gulf with maximum wave heights up to 10 ft, as a strong cold front drops southward over the western Gulf of Mexico waters and southeastern Mexico. The tight pressure gradient over southeastern Mexico will keep this winds in the 20 to locally 30 kt range through Friday evening, with maximum wave heights building to around 11 ft. Gale force winds are expected to begin Fri evening and increase further to 45 kt Sat and Sat night, possibly reaching storm force early Sun in what looks like an extended gap wind event into next week. Baja California Norte Gale... The NW winds to gale force over the Gulf of California will veer more N and NE late today and tonight. NE gales will funnel through lower lying areas over Baja California Norte into the Bay of Sebastian Vizcaino, roughly between Santa Rosalita and Puerto Canoas late today and tonight. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N85W to 06N95W where it transitions to the intertropical convergence zone and continues to 08N100W to 09N130W. Scattered moderate convection from 06N to 08N between 95W and 100W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Along with winds to gale force near the coast listed above, the main issue in the near term will be strong to near gale force NE winds late today and tonight emerging off the coast of Baja California south of 30N, reaching nearly 500 nm into the Pacific open waters with seas of 8 to 12 ft by early Fri. The winds will diminish by Fri night, with seas subsiding below 8 ft off the coast of Baja California through late Sat. Elsewhere gentle to moderate winds and 4 to 6 ft seas will persist through into next week. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Gentle to moderate gap winds will occasionally pulse to fresh gap winds through the Gulf of Papagayo though Sat morning. Strong high pressure building north of the area behind a cold front penetrating into the western Caribbean will allow strong gap winds by Sat night, reaching near gale by Sun night into Mon, with seas building to 11 ft downstream. Elsewhere, light to gentle N to NE winds are expected N of the monsoon trough, and mainly gentle to moderate S to SW winds are expected to the S of the monsoon trough. Seas are in the 5 to 7 ft range in SW swell this evening to the S of the monsoon trough, and will subside to 4-6 ft through mid week. Large NW swell with wave heights of 8-10 ft from the upcoming Tehuantepec gap wind event will spread across the offshore waters of Guatemala late this week and over the weekend. Localized gap wind pulses of 20 to 25 kt are possible off the coast of El Salvador and Guatemala starting Sat night. REMAINDER OF THE AREA... An earlier scatterometer satellite pass indicated fresh to strong SE winds north of 28N and within 120 nm east of a cold front pushing into the discussion area, currently reaching from 30N137W to 21N140W. Scattered showers are noted along the front currently. The front will stall shortly and start to dissipate, but associated long period NW swell will continue to propagate into the region, encompassing the area north of 12N and west of 125W tonight, and most of the region west of 120W by Fri night. The longer period NW swell will mix with shorter period NE swell and wind waves by Fri night over the area north of 20N and east of 125W. A surface trough from 20N129W to 10N133W is drifting westward. A tight pressure gradient will develop N and NE of this trough between it and strong high that shifts eastward over the central and NE waters. This will lead to a brief period of NE to E 20 to 25 kt winds from 18N to 22N between 127W and 130W this evening with induced wave heights of 8-10 ft. The trough dissipates and the winds diminish tonight, with residual local easterly wind waves merging with longer period NW swell. $$ Christensen