000 AXPZ20 KNHC 171521 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1521 UTC Wed Aug 17 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 1200 UTC surface analysis and satellite imagery through 1500 UTC. ...TROPICAL WAVES... A tropical wave is along 87W north of 10N moving west at 15 to 20 kt. Associated convection is described in the section below. The convection will gradually propagate from the Gulf of Papagayo and Gulf of Fonseca region toward the Gulf of Tehuantepec region during the remainder of the week. A tropical wave is along 103W to the north of 10N moving west at about 10 to 15 kt. Associated convection is described in the section below. The tropical wave is expected to gradually become absorbed with the broad circulation of another tropical wave and area of low pressure ahead of it along 107W. A tropical wave is along 107W from 10N to 19N through a developing area of low pressure near 14.5N107W moving west at around 10 kt. Scattered moderate convection is within 150 nm in the southwest quadrant of the low. Overnight scatterometer data indicated fresh to strong winds and seas of 8 to 10 ft within 180 nm in the southeast quadrant of the low, with a surrounding area of 8 to 9 ft seas from 08N to 14N between 100W and 115W in southwest swell. The associated winds and seas will persist as the low reaches to near 18N111W by 48 hours. A tropical wave is along 130W from 11N to 20N through a weakening area of low pressure near 15.5N130W moving west at around 10 kt. Scattered moderate convection is within 150 nm in the north quadrant of the low. Associated winds on the northwest to north side of the low are up to fresh levels due to a tighter pressure gradient between the lower pressure and high pressure ridging to the north. These fresh winds combined with long period southwest swell is supporting an area of combined seas to 8 ft. The low will eventually move west of 140W by 48 hours with all associated convection moving west of 140W by then. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 11N85W to 14N94W to 14N100W, then resumes from low pressure near 14N107.5W to 09N125W, then resumes from low pressure near 15.5N130W to 12N140W. Scattered moderate convection is from 05N to 08N east of 88W, within 180 nm south of the monsoon trough axis east of 91W, and also north of a line from 13N93W to 10N101W to 18N108W to 24N108W, which is associated with a pair of passing tropical waves, and the low pressure area near 14N107.5W. ...DISCUSSION... North of 15N east of 120W: A ridge axis extends southeastward into the area from 23N120W to near the Revillagigedo Islands. A relatively weak pressure pattern prevails across the area with surface troughing extending from north to south along or just offshore of the Baja California peninsula. As a result, light to moderate mainly northwesterly flow prevails along with combined seas of 5 to 7 ft. Low pressure currently near 14N107.5W will move northwest and pass between Socorro and Clarion Islands on Friday, then continuing northwest thereafter. At a minimum, fresh to strong winds and seas of around 8 ft could accompany the low on mainly the southeast side, although model disagreement remains from Friday through Sunday. South of 15N east of 120W: A locally tight pressure gradient prevails within 60 nm of shore west of the Tehuantepec region due to high pressure over interior Mexico and 1007 mb low pressure near 14N107.5W. The low is described in more detail in the tropical wave section above. The area of fresh to strong winds will shift northwest along the coast of Mexico concurrent with the movement of the low. Northerly winds will pulse to fresh to strong in the Gulf of Tehuantepec late tonight into early Thursday, then to fresh levels during the overnight hours of Thursday night and Friday night. Otherwise, mainly light to moderate winds will prevail on either side of the monsoon trough, except pulsing to moderate to fresh in the Gulf of Papagayo during the overnight hours with nocturnal drainage flow. Combined seas of 4 to 7 ft will prevail through the end of the week, subsiding slightly this weekend. West of 120W: High pressure of 1033 mb centered well north of the area near 42N140W extends a ridge southeastward through 30N134W to 23N120W. The pressure gradient between the ridge and inverted low pressure troughing over mainly northern California is generating gale force northerly winds offshore of the Redwood Coast. These winds will generate and send fresh northerly swells into the area to the north of 29N later this morning through the end of the week, with the seas decaying to less than 8 ft this weekend as the winds diminish. Elsewhere, moderate to fresh winds can be found, along with combined seas of 4 to 7 ft. The ridge will break down this weekend with a new ridge becoming oriented from 30N128W to new high pressure at 1016 mb near 25N130W to 25N140W by Sunday morning as the remnants of a cold front drop into the far northwest portion of the area. This will result in a weaker pressure gradient across the region allowing for trades to diminish slightly. $$ LEWITSKY