000 AXPZ20 KNHC 162127 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1909 UTC Thu Jun 16 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 1800 UTC surface analysis and satellite imagery through 2100 UTC. ...SPECIAL FEATURES... A weak and broad 1008 mb low pressure area is centered near 16.5N 107W and is moving to the northwest around 8 kt. Scattered moderate convection is within 180 nm in the east quadrant and also within 360 nm in the south quadrant. Convection near the center has been intermittent as has been the case for the past 48 hours or so. Recent scatterometer data sampled the low and surrounding area. This data indicates a swath of fresh to strong winds located well away from the center offshore of southwest Mexico. These winds are likely due to funneling up against high terrain, with only light to moderate winds noted near the actual center. Recent altimeter data sampled 7 to 9 ft seas surrounding the low, 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 along 85W to the north of 10N moving westward around 10 to 15 kt. The wave axis extends across central Nicaragua and eastern Honduras. Satellite imagery indicates limited convection with this tropical wave over the northeast Pacific waters with the convection confined to the northwest Caribbean Sea and adjacent land areas. ..INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from low pressure near 16.5N107W to 09N120W to 09N135W. The intertropical convergence zone axis extends from 09N135W to 07N140W. Scattered moderate convection is within 240 nm to the southeast of a line from 11N97W to 08N104W, and also within 120 nm either side of the axis between 113W and 138W. ...DISCUSSION... From 15N northward and from 120W eastward: Weak high pressure ridging extends into the area to the west of 110W from 28N120W to 19N110W. Low pressure is located just to the southeast of the terminus of the ridge. This low is described in great detail in the special features section above. Mainly moderate northerly flow and combined seas of 5 to 7 feet cover the waters to the west of 110W. These conditions are forecast to persist through Friday night. Winds will increase offshore of southern California and the northern Baja California peninsula by Saturday morning as the pressure gradient tightens. Fresh northwest flow to the north of 28N will support building seas to 8 feet. 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 17N116W. 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 Monday morning and Tuesday morning. The increasing winds will be due to the combination of nocturnal drainage flow along with the passage of tropical waves. 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 pre-frontal trough has breached 30N140W, currently analyzed from 30N137W to 28N140W. The cold front is analyzed around 60-75 nm to the northwest of this pre-frontal trough. These features 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 and trough will merge and stall from near 30N130W to 25N139W by Friday 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. $$ JLewitsky