AXPZ20 KNHC 200239

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0405 UTC WED SEP 20 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 0000 UTC surface analysis and satellite imagery through 0130 UTC.


Post-Tropical Cyclone NORMA near 22.1N 115.6W 1007 MB AT 0300 UTC moving WNW or 290 DEG at 6 KT. Maximum sustained winds 30 KT gusts 40 KT. Isolated light to moderate convection is within 90 nm across the S semicircle. The low level circulation of Norma has begun to decouple or separate from the middle level circulation, and convection is now very meager. Norma has lost tropical characteristics and is now post-tropical. The remnant low will continue to move slowly NW for the next few days. Associated winds and seas will slowly wind down before the low dissipates Thu.


A tropical wave is propagating across the eastern waters just to the west of the Gulf of Tehuantepec, along 96W N of 07N. Scattered moderate to strong convection is from 10N to 16N between 92W and 104W. Global models suggest that a low pressure center could develop across this region in a few days as active convection continues.


Monsoon trough extends from 09N74W TO 08N82W TO 13N96W TO 10N107W TO 13.5N132W TO BEYOND 13N140W. Scattered moderate convection is from 03N to 08N between 77W and 84W. Scattered moderate to strong convection is from 06N to 13.5N between 77W and 89W. Scattered moderate to strong convection is from 12N to 16N between 132W and 138W.



A broad surface ridge extends SE into the region and passes through 32N128W to near 25N118W. Anticyclonic wind flow covers the area N through NW of the remnant lows of Norma and Otis. A surface trough is in the northernmost part of the Gulf of California, where fresh northerly winds prevail across the nearshore waters of Baja California Norte. The surface pressure gradient that exists between the ridge and the trough is supporting gentle to moderate N to NE winds, and seas in the range from 5 feet to 7 feet. The ridge will build during the middle of the week as the remnants of Norma dissipate, which will freshen winds off the Baja California coast with seas building to 6 to 8 feet.


A tropical wave across the W Caribbean is moving slowly into the far eastern waters. Light to gentle monsoonal flow prevails to the south of the monsoon trough, while gentle to moderate southeasterly winds prevail to the N of the monsoon trough between 90W and the Gulf of Tehuantepec. Light to gentle northeasterly winds will briefly develop to N of the monsoon trough Tue night before the trough lifts N and along the coasts. S to SW swell continues to propagate across the area with seas in the 6 to 8 foot range from 100W westward, and in the 4 to 6 foot range from 100W eastward.


Post-Tropical Cyclone OTIS near 18N129W 1008 MB moving WSW at 5 KT. Maximum sustained winds 30 KT gusts 40 KT. No convection is associated with the remnants of Otis at this time. However, sufficient pressure gradient exists between this low center and a surface ridge to the NW to create strong NE to E winds 20 to 25 kt WITHIN 180 NM across the NW SEMICIRCLE, where seas are 8 to 11 ft. The low will continue to move WSW during the next 2 days and gradually dissipate, with an area of fresh to strong NE to E winds and seas 8 to 9 ft accompanying it through Thu.

A 1030 mb high pressure center is located near 38N148W and extends S and SE into the waters N of 25N. The surface pressure gradient that exists between this high pressure, and the lower pressure that is in the vicinity of the monsoon trough, will maintain moderate to fresh trade winds to the N of 20N west of 120W, and to the NW of Otis remnants, with seas in the 6 to 9 foot range. The ridge will prevail in the northern waters during the next few of days with these general conditions persisting.

$$ Stripling