Tropical Storm Hagupit maintained its intensity on Tuesday as it moved farther away from the Philippines.  At 10:00 p.m. EST on Tuesday the center of Tropical Storm Hagupit was located at latitude 13.3°N and longitude 116.6°E which put it about 320 miles west-southwest of Manila, Philippines and about 475 miles east-northeast of Cam Ranh, Vietnam.  Hagupit was moving toward the west at 13 m.p.h.  The maximum sustained wind speed was 50 m.p.h. and there gusts to 65 m.p.h.

Thunderstorms continue to develop near the center of circulation and upper level outflow is evident on satellite images.  However, Hagupit is likely to move into a more unfavorable environment as it moves westward.  Northeasterly winds over the lower levels of the South China Sea contain cooler and drier air.  Some of the cooler, drier air may be getting pulled around the western and southern portions of Hagupit’s circulation.  If the drier air reaches the center of circulation, then deep convection will diminish and the wind speeds will decrease.  Hagupit is also likely to move into an area of more vertical wind shear as it moves westward, which could weaken the storm even faster.

Hagupit is currently being steered westward by a subtropical ridge located north of it.  If Hagupit weakens and the convection becomes shallower, if could be steered toward the southwest or west-southwest by the northeasterly winds in the lower levels.  The center of Hagupit could near the coast of Vietnam in about 36 hours.

Tropical Storm Hagupit has moved across the central Philippines and it is now beginning to move into the South China Sea.  At 10:00 p.m. EST on Monday the center of Tropical Storm Hagupit was located at latitude 13.5°N and longitude 119.9°E which put it about 100 miles southwest of Manila.  Hagupit was moving toward the southwest at 11 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.

Some thunderstorms have redeveloped near the center of Hagupit now that it is back out over open water.  It is possible that the tropical storm could maintain its intensity or even strengthen a little in the short term.  However, as Hagupit moves farther west it will encounter a northeasterly flow of cooler and drier air and more pronounced vertical wind shear.  The more unfavorable thermodynamic environment and wind shear will likely cause Hagupit to weaken during the next few days.

The northeasterly winds are expected to push a weakening tropical storm or depression in the general direction of southern Vietnam.  Hagupit or its remnants could make landfall in Vietnam in about 72 hours.

Hagupit has weakened below typhoon intensity and it is now a tropical storm.  At 10:00 p.m. EST on Sunday the center of Tropical Storm Hagupit was located at latitude 13.4°N and longitude 112.7°E which put it near Catanauan, Philippines and about 140 miles southeast of Manila.  Hagupit was moving toward the northwest at 7 m.p.h.  The maximum sustained wind speed was 70 m.p.h. and there were gusts to 85 m.p.h.

Interaction of the circulation with land and moderate vertical wind shear have gradually reduced the intensity of Hagupit and the weakening trend should continue on Monday.  Once Hagupit moves west of the Philippines, it will move into an area of stronger northeasterly winds in the lower levels and cooler, drier air.  As a result the rate of weakening could increase.

There are indications that Hagupit could begin to move toward the southwest when it encounters the stronger northeasterly flow.  A much weaker Hagupit or its remnants could reach southern Vietnam in a few days.

Tropical Depression 21W (TD 21W) is bringing rain to parts of the Central Philippines as it moves toward the west-northwest.  At 7:00 p.m. EST on Wednesday the center of TD 21W was located at latitude 9.8°N and longitude 122.9°E which put it about 70 miles east of Cebu and about 350 miles south-southeast of Manila.  TD21W was moving toward the west-northwest at 20 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and there were gusts to 45 m.p.h.

TD 21W appears to be developing some spiral bands of showers and thunderstorms and it could become more organized as it moves away from the Philippines.  It is over warm Sea Surface Temperatures and upper level outflow appears to be developing.  As a result of those factors TD 21W could intensify into a tropical storm during the next 24-36 hours.  Available guidance suggest that TD 21W will continue to move in a general west-northwesterly direction and it could approach the coast of Vietnam in about three days.