Tropical Update

A developing low pressure area was spotted today near the Marianas Islands. Invest 91W was last located approximately 600km north northwest of Guam. The disturbance, together with an upper level feature, is bringing widespread rains across the islands; some places here, particularly north of Guam, have reported 30 to 60mm of rain in the past 24 hours.

IR Image from NOAA

The JTWC is currently giving 91W a MEDIUM chance of development because of the very warm sea surface temperatures and weak to moderate wind shear. Latest satellite analysis from this morning reveals a well-defined low level circulation center characterized by an asymmetrical wind field with 30 to 40kph winds found on the eastern side while the western half is dominated by weaker winds of around 10 to 20kph. There are two competing TUTT (Tropical Upper Tropospheric Trough  features surrounding 91W. The first one, located to the west, is bringing upper-level convergence which is limiting convection. On the other hand, the TUTT north of 91W is enhancing outflow as well as convective activity, particularly on the eastern half.

Computer models are split regarding the ultimate track of 91W. What we do know is that the disturbance should not move greatly in the next 2 days due to a blocking feature near China. However, it's still up in the air whether 91W can consolidate and become a depression. Furthermore, if it does, it's still hard to tell where this will end up.

Elsewhere, a weak Tropical Wave is moving across Mindanao today bringing widespread rains across Mindanao, Visayas, and Palawan. For Luzon, afternoon thunderstorms will continue to pop-up intermittently especially in the afternoon and evening hours.

We'll have another update on 91W tomorrow.
______________________________________________
Issued (0930 UTC) 530pm PhT 071412