000 AXPZ20 KNHC 191835 TWDEP Tropical Weather Discussion...updated NWS National Hurricane Center Miami FL 1835 UTC Wed Apr 19 2017 ...updated convection under ITCZ/Monsoon Trough section 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 1800 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough axis extends from 06N84W to 05N95W to 04N105W. The intertropical convergence zone axis extends from 05N108W to 06N123W to 04N131W to 02N123W to beyond 02N140W. Scattered moderate/isolated strong convection is within 180 nm north of the axis between 84W and 87W, and within 60 nm of the axis between 87W and 93W. Scattered moderate convection is within 120 nm north and 60 nm south of the ITCZ axis between 108W and 120W, and also within 60 north of the ITCZ axis between 130W and 134W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A surface ridge extends from 1024 mb high pressure centered near 32N128W to near 19N115W. Northwest winds have increased to fresh to strong over the offshore waters west of Baja California Norte where the pressure gradient is tight. These winds are accompanied by seas to 8 ft. The fresh to strong winds will spread southward over much of the offshore waters of the Baja California Peninsula through Thursday evening as the high pressure ridge strengthens some. As a result, combined seas will build to 8 to 11 ft through early Friday afternoon. The pressure gradient will then slacken on Friday and Saturday and allow winds and seas to diminish as a cold front weakens the ridge to the west. In the Gulf of California south of 29N, gentle to moderate northwest winds will increase to moderate to fresh this afternoon through Friday with the added ingredient of late afternoon heating possibly leading to local enhancement of winds. Winds will be light to gentle north of 29N through Thursday as surface troughing developing over far northern Baja weakens the pressure gradient. A minor tightening of the gradient is then expected to increase these winds to moderate to fresh category on Friday. Seas will be 2 ft or less, except for a pocket of 2 to 4 ft seas in the central portion through Thursday night, and in the northern portion on Friday due to the winds there increasing to moderate to fresh category. In the Gulf of Tehuantepec, fresh to strong northerly winds are expected late tonight and into Thursday. Winds over the Gulf then become light and variable through Friday, with a possible brief instance of moderate north winds during the morning on Friday. Beyond the discussion forecast time, models guidance continue to suggest that the significant northerly gap wind event is expected to begin late Sunday afternoon as a relatively strong cold front for this time of year pushes south along the Sierra Madre Oriental mountains. Models depict strong to minimal gale force winds starting Sunday night through Monday morning, with seas building to around 12 or 14 ft. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... In the Gulf of Papagayo, moderate nocturnal drainage winds will become light and variable this afternoon, and change little through Friday. In the Gulf of Panama, light to moderate northwest winds will become mostly light south to southwest winds this afternoon and light and variable winds Thursday night and Friday as models are depicting that broad low pressure will continue to encompass the eastern portion of the area through that time period. Elsewhere, light to gentle winds and combined seas of 3 to 6 ft mainly due to mixed long period southwest and northwest swell will change little through Friday. REMAINDER OF THE AREA... A 1024 mb high pressure system is centered near 32N128W with a ridge extending southeastward to the near 19N115W. A weakening trough, remnants of a previous front, is analyzed from near 29N127W to near 21N137W. The leading edge of northwest swell producing peak wave heights of 12 ft, and that propagated into the area behind recent fronts has spread southeastward to west of line from 32N125W to 25N132W to 21N140W. This swell will propagate further southeastward reaching south to 06N and west of 113W by Thursday evening, and to near 05N between a line from 22N111W to 15N115W to 05N122W and another line from 32N127W to 24N137W to 20N140W by Friday. This swell will slowly begin to decay late Friday into Saturday. The next cold front to affect the northwest section of the area will begin to approach the far northwest corner late Thursday night into Friday. A tightening pressure gradient ahead of this front will develop strong southerly winds to the northwest of a line from near 32N137W to 29N140W at that time with seas of 8 ft. These winds will spread eastward to near 134W on Friday with seas building to 10 ft. The front will also usher in another round of northwest swell over the northwest portion of the area later on Friday as the front weakens, with seas to 10 ft there. A recent southerly swell event that migrated into the area the past few days will be confined to south of 01S between 103W and 119W inducing seas of 8 ft late this afternoon. This swell will then cover the area to the south of a line from 01S120W to 04N110W to 02N101W to 03.4S97W by early on Thursday, and to the south of a line from 02S117W to 02N109W to 03.4S102W on Friday morning. Otherwise, the pressure gradient to the southwest of the aforementioned high pressure ridge will maintain generally fresh northeast to east winds from near 06N to 20N west of 120W, and mainly gentle to moderate northeast to east winds south of 06N. These winds will support seas of 8 to 9 ft from 05N to 13N between 115W and 135W through early on Thursday. These seas will then merge with the large set of northwest swell propagating southeastward described above on Thursday evening. $$ Aguirre