000 AXPZ20 KNHC 081601 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Tue Aug 8 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 1200 UTC surface analysis and satellite imagery through 1530 UTC. ..TROPICAL WAVES... A tropical wave axis is along 109W from 08N to 19N, moving westward 12 knots. The latest satellite-derived high density winds are showing cyclonic turning in this area. First visible satellite imagery shows some cyclonic turning of the low cloud field as well within about 90 nm either side of the wave axis. Scattered moderate convection is present within 120 nm west of the wave from 09N to 10N. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from along 10N79W to 12N92W to 14N100W to 08N130W. A second segment of the monsoon trough extends from 13N130W to low pressure near 13N137W 1012 mb and to beyond 11N140W. Scattered moderate isolated strong convection is within 180 nm south of the axis between 104W-107W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A 1011 mb low pressure center, remnants of former Tropical Depression Eleven-E, is near 20N112W. It is drifting southward. Latest satellite imagery shows that this low is quickly weakening. Isolated showers are possible within 60 nm of the low. It is forecast to become a trough by late Wednesday, and drift south-southeastward to near the Revillagigedo Islands by late Thursday. The pressure gradient resulting from the combination between high pressure west of the Baja California peninsula and lower pressure over the SW U.S. and Baja California is allowing for moderate to locally strong winds northeast winds to exist across these waters. Seas associated with these winds are in the 4 to 6 ft range. Scattered moderate isolated strong convection that moved offshore the coast of Mexican earlier this morning from 17N-19N and west to 107W is weakening, and will continue to do so through this afternoon. Similar nocturnal activity is expected to develop again tonight just inland central Mexico from near 17N-21N, and move offshore under strong northeast upper level flow. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate southerly winds are expected to the south of the monsoon trough, with gentle and variable winds to the north of the monsoon trough. Sea heights generally will range from 4 feet to 6 feet. A set of long-period southerly swell has arrived to the coastal areas of Costa Rica and Panama, and could be producing occasional seas to the range of 6 to 7 ft as waves reach the shallow waters along the coast. Swell model guidance indicates that the swell energy will begin to dissipate later this morning and through Wednesday allowing for the 6 to 7 ft seas to slowly subside. Scattered strong convection is over the Gulf of Tehuantepec within 30 nm of 16N94W. This activity is expected to last through the afternoon, and possible evening hours. REMAINDER OF THE AREA... A surface ridge is forecast by the global models to build southeastward through Thursday as the parent high, that is located well to the northwest of the area, drops southeastward. This will push the remnant low of Tropical Depression Eleven-E southeastward toward the Revillagigedo Islands, that are to the west of central Mexico, as it weakens and becomes a surface trough. The pressure gradient between the ridge and lower pressure near the monsoon trough region will allow for moderate to locally fresh trade winds from about 12N to 19N and west of about 129W, along with resultant seas in the range of 5 to 6 ft until Saturday night. A 1011 mb low pressure center is along the monsoon trough at 13N137W. This low is forecast to weaken in 24 hours as it tracks in a general westward direction along the monsoon trough, eventually moving west of 140W on Wednesday afternoon. A second low pressure of around 1011 mb is forecast to form along the monsoon trough near 12N130W by early on Wednesday, and track westward to near 12N135W by Thursday evening. No significant organization is expected with either of these lows. Wave model guidance is forecasting a large southerly swell train, with 8-9 foot wave heights crossing 03.4S from 120W eastward on Friday evening in 3 days, and moving northward and reaching the Equator just after midnight on Sunday. Sea heights ranging from 8 feet to 9 feet are forecast to reach the coastal waters of Panama and Costa Rica between 79W and 87W, and the coastal waters of Guatemala, around daybreak on Sunday. The overall areal coverage by late Monday is expected to be confined from 02N to 07N between 81W and 86W, and from 05N to 16N between 90W and 114W. $$ Aguirre