000 AXPZ20 KNHC 131604 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Thu Apr 13 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 1545 UTC. ...SPECIAL FEATURES... ...Gulf of Tehuantepec Gale Warning... The combination of high pressure over the eastern and southeastern sections of Mexico, and lower pressures present to the south of the Tehuantepec region continues to be tight enough to support minimal gale force north to northeast winds over a narrow swath of area across the Gulf of Tehuantepec. First few visible satellite imagery reveal low cloud streamers emanating from both the eastern and western edge of the Gulf indicative of the ongoing gap event. Seas associated with these wind conditions are in the 8 to 11 ft range. The gale force winds will continue through the rest of the morning, then diminish to fresh to strong in the afternoon. Fresh to strong northerly flow will then pulse, mainly at night with the aided influence of nocturnal drainage flow, through the upcoming weekend. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The intertropical convergence zone axis extends from 03N90W to 04N104W to 03N114W to 03N122W to 02N130W to 02N140W. Scattered moderate to strong convection is within 60 nm north of the axis between 124W and 129W. Scattered moderate/isolated strong convection is within 60 nm north of the axis between 119W and 124W. Scattered moderate convection is within 120 nm north of the axis west of 134W, and also south of 02S between 114W and 120W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... See the Special Features section for details on the Gulf of Tehuantepec Gale Warning. A surface ridge extends from northwest to southeast across the offshore waters. Scatterometer data from overnight last night depicted northwest fresh to strong winds offshore of Baja California Norte where seas are up to 8 ft. The pressure gradient will remain tight enough to support these conditions through Friday night, then will weaken thereafter. In the Gulf of California, mainly light to gentle variable flow will prevail through the upcoming weekend, with seas mainly 2 ft or less, except 3 to 4 ft near the entrance to the Gulf. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... In the Gulf of Papagayo, fresh to locally strong nocturnal drainage winds expanded to the north early this morning reaching to just west of the Gulf of Fonseca based on an observations from ship ZCEF3. These winds are forecast to diminish to the fresh category by early this afternoon, then pulse back up to the strong range late tonight and diminish to the fresh range early in the afternoon on Friday. Seas are expected to build to 8 ft with these winds. These gap winds will pulse again to the strong category Friday and Saturday night with seas up to 8 ft. In the Gulf of Panama, moderate to fresh nocturnal northerly flow is expected during the overnight hours through the upcoming weekend. Seas will be in the range of 5 to 6 ft downstream of the Gulf. Elsewhere, light to gentle winds and combined seas of 3 to 6 ft will change little through the weekend. REMAINDER OF THE AREA... A dissipating cold front is analyzed over the north-central and northwest section of the discussion area from near 32N124W to 26N133W to 26N1402W. The southern segment of a reinforcing cold front just north of the area reaches southwest to near 27N135W. The second front will merge with the remnants of the dissipating front this evening and dissipate early on Friday over the far northeast waters. A large set of northwest swell producing seas of 8 to 11 ft will propagate into the northwest portion through tonight, and through the north-central and northeast portions Friday through Saturday while losing energy. Seas are forecast to subside to 8 to 9 ft by Saturday night in the far northeast portion off the far northern portion of Baja California Norte. Models are suggesting that a stronger cold front will approach the far northwest corner early on Saturday, then move over that same northwest corner during Saturday. Southerly winds ahead of the front are expected to be in the range of 20 to 25 kt north of about 29N. Wave model guidance indicates that this next front will usher in a new set of northwest swell that will build seas to the range of 8 to 10 ft in the far northwest portion of the area on Saturday, but then slowly subside late on Saturday into Sunday as the swell energy decays. Elsewhere, a ridge axis extends from a 1021 mb high pressure center analyzed at 27N129W east-southeastward to near the Revillagigedo Islands. The pressure difference between the ridge and lower pressures found to the southwest of the ridge is allowing for generally fresh to locally strong northeast trades to exist from about 07N to 14N west of 120W, and for mainly fresh trades from 04N to 17N between 117W and 135W. Seas are 9 to 11 ft in the area of fresh to locally trades and 8 to 9 ft in mixed northeast and northwest swell within the area of fresh trades. The 1021 mb high is forecast to dissipate by early on Friday. This will bring a weakness to the tight pressure gradient bringing a diminishing trend to the fresh to locally strong trades. However, seas of 8 to 10 ft in mixed northeast and northwest swell are forecast from 04N to 15N west of 117W at that time. Another area of high pressure will build across the area during Friday, but will be shunted to the east with the approach of deep layer troughing from the west and the associated aforementioned cold front. This process will bring a further weakening to the trades Saturday and Saturday night, with model guidance showing mostly gentle to moderate trades with pockets of fresh trades over the western and central waters from about 05N to 20N. The seas of 8-9 ft within these areas of trades will gradually shrink in size on Saturday. A broad mid to upper trough observed on water vapor imagery and in the NWP models is situated north of the equator between 85W and 104W. A couple of shortwave troughs are noted rounding the base of this trough. Satellite imagery shows scattered moderate/isolated strong convection from 03N to 06N between 90W and 95W, and also within 30 nm of 04N96W. This activity is likely to persist into this evening, with a good possibility of new convective activity redeveloping late tonight into Friday. $$ Aguirre