000 AXPZ20 KNHC 180246 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Thu Aug 18 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 0000 UTC surface analysis and satellite imagery through 0230 UTC. ...Special Features... A tropical wave axis is along 108W from 11N to 19N. Low pressure of 1006 mb is along the wave near 16N108W. This system is moving northwest at 10 kt. Latest satellite imagery shows that the system consists of a broad circulation, and the low near 16N108W is rather small, and removed to the east of where deep convection is occurring. This convection consists of scattered moderate to isolated convection from 12N to 16N between 110W and 112W. Scattered moderate convection is also within 30 nm of 15N107W. Upper level winds are currently not favorable for this system to organize tonight, but are expected to become marginally conducive for the low to gradually develop Thursday and Friday with a medium probability of tropical cyclone formation. A swath of strong southwest winds within 180 nm in the southeast quadrant with seas of 8 to 10 ft is forecast to transition into 150 nm in the northeast semicircle and 60 nm in the southwest semicircle by Friday evening. An area of 8 to 9 ft seas in southwest swell is from 08N to 14N between 100W and 115W in southwest swell. The associated winds and seas will persist as the low reaches to near 19N112W by 48 hours with a forecast pressure of 1005 mb. ...TROPICAL WAVES... A tropical wave axis is along 90W north of 10N moving west at about 17 kt. Clusters of scattered moderate to isolated strong convection are moving offshore southeastern Mexico, Guatemala and El Salvador. Isolated weak convection is elsewhere within 60 nm west of the wave. A tropical wave is along 131W from 11N to 19N moving westward at 10-15 kt. A small and weak low of 1007 mb is on the wave near 16N131W. Only isolated showers and weak isolated thunderstorms are within 60 nm of the low. A shrinking area of long period mixed swell is producing seas to 8 ft within the points from 17N131W to 16N131W to 17N133W to 17N131W. This area of swell is forecast to gradually dissipate as it migrates to the far western portion of the area in 48 hours. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 10N85W to 09N90W TO 12N98W. It resumes from low pressure near 16N108W to 12N118W to low pressure near 09N125W 1008 mb. The trough axis then extends from 12N131W to beyond 12N140W. Scattered moderate to strong convection is south of the axis within 60 nm of a line from 08N78W to 08N83W. Scattered moderate convection is within 120 nm south of the axis between 110W and 114W. ...DISCUSSION... North of 15N east of 120W: A weak 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 15N107W will move northwest and pass between Socorro and Clarion Islands on Friday. The low is forecast to continue on a generally northwestward track thereafter with some slow development possible. Fresh to strong winds and seas of 8 to 9 ft are forecast within 180 nm in the southeast quadrant of the low. These conditions may possibly increase by Friday pending development of the low. South of 15N east of 120W: A locally tight pressure gradient prevails is within 60 nm of the Mexican coast west of the Tehuantepec region due to the combination of high pressure over interior Mexico and the 1006 mb low pressure near 16N108W described in the special features section above. The ensuing fetch is bringing seas to 8 ft in a southeast swell there as was earlier reported by ship "VRGA6" at location 15N97.5W. The persistence of this tight gradient is forecast to lead to strong southeast winds within 60 nm of the coast of Mexico between 103W and 105W on Thursday with seas of 8 to 9 ft. Model guidance indicates that the gradient will weaken by Thursday as the low pressure moves farther to the northwest. Northerly winds will marginally pulse to fresh to strong in the Gulf of Tehuantepec by early Thursday morning with seas building to 6 to 8 ft, 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 Friday. West of 120W: High pressure of 1034 mb centered well north of the area near 46N139W 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 have ushered fresh northerly swells into the area to the north of 29N between 126W and 134W. These conditions are forecast to diminish on Friday as the culprit pressure gradient weakens. $$ Aguirre