000 AXPZ20 KNHC 171006 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Fri Jun 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 0600 UTC surface analysis and satellite imagery through 0945 UTC. ...SPECIAL FEATURES... A weak and broad 1008 mb low pressure area is centered near 17N 108W and is moving to the northwest around 7 kt. Scattered moderate convection is within 90 nm in the east semicircle and within 200 nm in the west semicircle. Convection near the center continues to be intermittent as has been the case for the past 48 hours or so. Seas surrounding the low are 8 to 10 ft, mainly due to mixed southwest and northwest swell combined with wind seas on the northeast side. The low still has a medium chance of tropical cyclone development during the next 48 hours. The low will gradually weaken thereafter as it moves over cooler waters. ...TROPICAL WAVES... A tropical wave axis is near 87W to the north of 10N moving westward around 10 kt within the last 24 hours. The wave axis extends across central Honduras and El Salvador. Satellite imagery indicates numerous moderate to isolated strong convection over the northeast Pacific waters N of 11N between 86W and 89W. ..INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 11N89W to a 1012 mb low near 09N97W to 09N102W. A second extension of the monsoon trough begins near 14N109W and continues along 10N120W to a 1013 mb low near 08N127W to 07N132W. The ITCZ axis extends from 06N133W to 07N140W. Numerous moderate to isolated strong convection is from 07N to 09N between 99W and 102W. Scattered moderate convection is from 07N TO 11N between 120W and 129W. ...DISCUSSION... From 15N northward and from 120W eastward: Weak high pressure ridging extends into the area to the west of 113W from 28N128W to 16N113W. Low pressure is located just to the east-southeast of the ridge. This low is described in more detail in the special features section above. Mainly gentle northerly flow and combined seas of 6 to 7 feet cover the waters to the west of 113W. These conditions are forecast to persist through tonight. Off northern and central Baja California, moderate northerly wind dominate as a result of a tighter pres gradient between the ridge and troughiness along the Gulf of California. These winds will further increase by early Saturday morning as the center of high pressure slightly strenghtens before dissipating near sunrise. However, a broad and stronger ridge will move N of the area increasing even more the pres gradient to support building seas to 8 feet Sunday. The area of fresh winds will shift to the west of 120W by Monday morning as broad troughing becomes defined from the northern Baja California peninsula southward to 21N107W. This troughing will drift west through the middle of next week with new high pressure developing near 21N115W by Tuesday night. In the Gulf of California, mainly tranquil marine conditions will prevail through the next several days. From 15N southward and from 120W eastward: Mainly light to moderate westerly flow will prevail, west to northwest to the north of the monsoon trough, and light to moderate to the south of the monsoon trough. These onshore winds will become offshore at night near the coastal areas due to nocturnal drainage flow. Model guidance continues to indicate offshore northerly flow increasing to fresh by Sunday morning in the Gulf of Tehuantepec, with similar conditions likely Tuesday morning. The increasing winds will be due to the combination of nocturnal drainage flow along with the passage of a tropical wave. These winds will build seas locally to 6 to 8 feet offshore of the Gulf of Tehuantepec. Combined seas are currently 4 to 6 feet as a long period southwesterly swell decays, however, a new southwest swell train will cross the Equator this weekend, propagating northeast through early next week. Combined seas will build to 7 to 9 feet Sunday morning beginning near 00N120W, gradually spreading to the northeast. Yet another reinforcing set of southwest swell will arrive quickly to help to push combined seas up to 8 to 11 feet by Wednesday morning. Elsewhere to the west of 120W: A cold front extends from 30N132W to 27N140W. This feature have weakened high pressure ridging which has allowed for trades to diminish slightly across the waters to the north of the ITCZ and monsoon trough. Combined seas are 5 to 8 feet to the south of 20N, and 4 to 6 feet to the north of 20N where winds are mainly light due to the weakened pressure gradient. The front will stall from near 30N130W to 25N139W this evening. This feature will then drift westward through Saturday, finally shifting to the west of 140W by Sunday morning as high pressure ridging rebuilds from the north. This ridging will then itself gradually shift westward through early next week as broad troughing approaches from the east. $$ Ramos