000 AXPZ20 KNHC 110920 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 920 UTC Tue Oct 11 2016 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 Tehuantepec Gale Warning...A tight pressure gradient continues between 1022 mb high pressure centered over east central Mexico and a 1008 mb surface low centered in the eastern Pacific near 11N97W. This is resulting in ongoing winds to gale force as verified by pair of vessels transiting the Gulf early this evening. The high pressure will weaken slightly and the low pressure to the south will move westward, allowing the gradient to weaken and winds to diminish slightly. Strong gap winds will continue however through mid week, mainly during the overnight hours when winds may reach 30 kt. Winds will diminish further through late week as a weak tropical wave moves into the region. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 10N86W to low pres near 10N98W the terminating near 12N110W. The monsoon trough resumes at low pressure near 15N120W to 10N128W to beyond 09N140W. Scattered moderate convection is noted within 90 nm north of the axis between 95W and 99W. Scattered moderate to strong convection is noted within 150 nm either side of the axis between 120W and 128W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A weak sub-tropical ridge axis extends northwest to southeast across the local Pacific waters from a 1018 mb high near 29N130W to off the southern tip of Baja California Sur. Light to gentle northerly breezes will persist across the region north of 20N through tonight, including the Gulf of California on the eastern periphery of the weak ridge. Winds off the coast of the Baja California peninsula will increase to 15 to 20 kt by Wednesday north of Cabo San Lazaro between building high pressure to the northwest and troughing over northwest Mexico. Elsewhere a light to gentle breeze, and 3 to 5 ft seas will persist. Scattered strong thunderstorms are occurring from offshore of the Gulf of Tehuantepec downwind to near 11N98W, where broad low pressure has developing along the monsoon trough near 11N96.5W. This active weather will shift westward and across 102W overnight. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate southwest winds persist from 05N to the monsoon trough which is meandering east to west along roughly 10N to 11N, with a light to gentle southwest breeze farther south toward the Galapagos Islands. Seas are 4 to 6 ft south of the monsoon trough largely in long period southwest swell. Little change is expected through mid week. Fresh to strong winds are expected to pulse higher at night across the Papagayo region but will not extend more than 90 nm offshore. Broad low pressure associated with the monsoonal circulation across the southwest Caribbean and Central America will produce light to moderate winds wavering from north to northwest from Guatemala to offshore of the Gulf of Papagayo for the next few days. REMAINDER OF THE AREA... The 1018 mb high pressure centered near 29N130W will move little and maintain the weak ridge extending eastward toward Cabo San Lucas. A stalled front is dissipating from 32135W to 25N140W with winds less than 20 kt on either side. Northwest swell generated behind this front has spread southeastward and well east of the stalled front, where seas are 8 to 9 ft north of 10N and west of 135W based on 0530 UTC altimeter data. The swell across this area will subside through today as it continues propagating southeast and merges with the trade wind belt. Elsewhere areas of moderate to fresh trade winds persist north of the monsoon trough to near 20N, with seas of 5 to 7 ft. Increasingly favorable conditions aloft are expected to enhance development of a 1008 mb low pressure area along the monsoon trough near 15N120W. The low pressure is expected to continue to develop through mid week as it moves northwestward, reaching 18N127W by early Wednesday accompanied by a 20 to 25 kt winds and 8 to 10 ft seas within 240 nm in the northern semicircle of the low. The low will weaken thereafter due to increased shear aloft. Another low pressure area downstream from the Gulf of Tehuantepec near 10N98W remains a second area of interest over the next several days, and is expected to continue to develop as it moves westward, crossing 120W by Wednesday night accompanied by fresh to strong winds and seas 8 to 9 ft within 120 nm in the northern semicircle of the low pressure. Looking ahead, there remains some uncertainty with regard to the strength of this low in the latter part of the week. The official forecast is a consensus showing little change in the intensity of the low pressure as it moves west across the region along roughly 15N to the south of the dominant ridge. A large area of long period northwest swell is expected to move into the region by mid week, with 8 to 12 ft seas covering the discussion area north a line from 30N115W to 11N140W by late Friday. $$ CHRISTENSEN