000 AXPZ20 KNHC 160220 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0220 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 0000 UTC surface analysis and satellite imagery through 0200 UTC. ...SPECIAL FEATURES... A weak and broad 1008 mb low pressure area is embedded in the monsoon trough near 14.5N 105.5W. This low is moving to the west- northwest at around 5 kt. Convection has gradually increased during the past several hours and become closer oriented to the center. Scattered moderate convection is within 480 nm in the east semicircle and within 240 nm in the nw quadrant of the low. Winds near the center are still likely light to moderate, however, a swath of fresh to strong winds are possible on the northeast side of the low well removed to the center, likely due to funneling effects up against the coast of southwest Mexico. Combined seas of 8 to 9 feet also surround the low. The low has a medium potential to develop into a tropical cyclone during the next 48 hours. ...TROPICAL WAVES... A tropical wave axis is along 85W to the north of 06N moving westward near 15 to 20 kt. The wave axis extends from the northwest Caribbean Sea and eastern Gulf of Honduras to across eastern Honduras, central Nicaragua, and western Costa Rica. Scattered moderate convection is within 75 nm of shore between 82W and 86W. ..INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 10N86W to low pressure near 14.5N105.5W to 10N114W to 10N125W. The intertropical convergence zone axis extends from 10N125W to 08N140W. Associated scattered moderate convection is within 120 nm either side of the ITCZ to the west of 110W. ...DISCUSSION... From 15N northward and from 120W eastward: A northwest to southeast oriented surface ridge is present over this section of the area. A low pressure center is near 15N and is described in great detail in the special features section above. The surface ridge will retract from southeast to northwest through Friday as the low pressure area advances across this part of the area. Outside of the nearby low pressure area, models indicate that mainly moderate winds will prevail through the remainder of the week, except occasionally pulsing to fresh offshore of the Baja California peninsula through the next several days. Combined seas of 5 to 7 feet will build to 7 to 9 feet to the north of 28N and to the west of the Baja California peninsula tonight through early Friday, then subsiding back to 5 to 7 feet through Saturday. The pressure gradient northwest of the area will tighten later this weekend, allowing for fresh northwest swell to arrive again and build combined seas back to 7 to 9 ft by late Saturday night through Monday, subsiding Monday night through the middle of next week. The Gulf of California: A surface trough will linger from northwest to southeast across the Gulf resulting in variable winds dependent on either side of the trough. The wind speeds will be light to moderate, with seas generally 2 feet or less away from the entrance of the Gulf. Little change is forecast through the rest of the week and continuing into the middle of next week. The Gulf of Tehuantepec: Mainly light onshore flow is anticipated, shifting to offshore during the overnight hours with nocturnal drainage flow through Friday, with seas of 5 to 7 feet subsiding to 4 to 6 feet late Thursday night. Offshore nocturnal flow is forecast to increase to fresh by late Friday night into early Saturday morning, then increase to fresh to strong late Saturday night into early Sunday morning as the local pressure gradient tightens. Similar conditions are then forecast for the following several nights/early morning hours. These increasing winds will temporarily build seas to 7 to 10 feet. From 15N southward and from 120W eastward: As described in the special features section above, low pressure near 15N will gradually move west-northwest out of this area. Otherwise, expect mainly gentle to moderate winds on either side of the monsoon trough, with primarily a westward/onshore component, except during the overnight hours when nocturnal drainage flow will result in offshore winds. Winds are forecast to increase to fresh to strong offshore of the Gulf of Papagayo late Monday night into early Tuesday as trades increase east of Central America in the western Caribbean Sea. These increasing winds will build seas locally to 6-9 feet by Tuesday morning. Cross-equatorial southwesterly swell will continue to propagate to the northeast with combined seas of 6 to 9 feet through tonight, subsiding thereafter. A new set of southwesterly swell will arrive at the equator and 120W by early Sunday, propagating to the northeast through early next week, with another and more significant southwesterly swell train arriving by the middle of next week. This quickly arriving reinforcing set of swell may build combined seas up to 8 to 12 feet by Wednesday afternoon. Elsewhere to the west of 120W: A surface ridge remains in the northern waters. The difference in pressure between the ridge and the lower pressure in the vicinity of the intertropical convergence zone will maintain moderate to fresh trade winds to the north of the ITCZ through Thursday afternoon. The surface ridge will then weaken Thursday night into Friday as a weak cold front or remnant trough slips into the far northern waters. This front/trough will stall in the far northwest portion by Friday morning, then will gradually retreat westward through Saturday, finally moving to the west of 140W Saturday night as ridging rebuilds from the north-northeast. As this ridging rebuilds, winds offshore of southern California will increase to fresh to strong due to the tightening pressure gradient. These winds will send fresh northerly swells into the area to the north of 25N and to the east of 130W Sunday through Monday. The ridging is then forecast to weaken and shift westward as broad troughing develops to the west of the Baja California peninsula by the middle of next week. $$ JLewitsky