Saturday, July 23, 2011

Tropical Depression Ma-On Update #23

Tropical Depression Ma-On is now moving northward, passing well east of Kanto. Ma-On was last located approximately 580km east southeast of Tokyo. Maximum sustained winds remain at 55kph with gusts of up to 85kph. Ma-On is moving north northeastward at 20kph

We have increased the winds a little bit for today's update in response to latest data and warnings. JMA is still classifying Ma-On as a Tropical Storm while JTWC is classifying the storm a Subtropical System. Both agencies have their wind estimates around 50-70kph. Furthermore, an ASCAT pass reveals Ma-On's closed circulation with winds of around 40kph around the system. Stronger winds of up to 80kph can be found on the northern quadrant of Ma-On. A thermal profile from NOAA still shows a warm core in the lower levels of Ma-On. Latest VIS and IR image though are showing some frontal and extratropical characteristics being exhibited by Ma-On.

We will still continue our updates for Ma-On as long as JMA continue to give theirs. We expect Ma-On to become extra tropical as early as Monday.

Moving on to the Philippine Sea, we still have the active monsoon trough affecting Visayas and Mindanao; it extends as far east as Eastern Micronesia (Chuuk). Within this trough are two disturbances that could potentially become cyclones next week: Invest 93W located about 650km east of Borongan, Samar, and Invest 94W drifting well away from the Philippines.

Invest 93W is located in a marginally favorable environment with high sea-surface temperatures and moderate vertical wind shear. Latest METAR from Koror reports winds from the southwest of around 20kph with a barometric pressure of around 1008mb. Convection is still unimpressive and low level convergence could be higher. Furthermore, moderate westerly winds of about 20kts just above the surface exist around this disturbance. Therefore, development of 93W will be slow as it detaches away from the trough.  Computer models, however, are still in excellent agreement in a cyclogenesis in this area. The consensus shows it becoming a weak tropical depression in two to four days' time. Long-range forecasts bring this future storm across extreme Northeastern Luzon (around Cagayan) by late next week as a Tropical Storm.

The same can be said for Invest 94W. Increasing convergence, weak to moderate wind shear (10-20kts), and high sea surface temperatures should allow 94W to develop slowly. Latest data puts the possible center near the 4 degree latitude. It needs to move north, away from the equator, to have higher chances of development based on climatology. Computer models are also bullish with regards to 94W and its development down the road. A weakness in the Subtropical Ridge by next week (which will be caused by Ma-On) should allow 94W to move generally northward. It could pass close to Northern Marianas late next week.

Issued (0730 UTC) 330pm PhT 072311

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