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Tropical Depression forms in the Philippine Sea; expected to enter PAR tonight

At 0600 UTC (2 pm Philippine Time), JMA–the official Regional Specialized Meteorological Center for the Western Pacific–had upgraded the low pressure area (Invest 99W) into likely the final tropical depression of the 2017 season.

According to JMA, the tropical depression was located near 9°N 136°E or about 225 km northeast of Melekeok, Palau or about 1035 km east-southeast of Surigao City, Philippines.  It was moving toward the west slowly with a central pressure of 1004 hPa.

20171230 0900 99W METSAT

At this time, forecast products are not being issued by PAGASA or JTWC.  The depression should enter the Philippine Area of Responsibility (PAR) overnight.  Once it does and PAGASA recognizes it as a depression, it will gain the local name “Wilma”.  Should it become a tropical storm, the international name would be “Bolaven” which was contributed by Laos to recognize a plateau in Champasak province which holds a significant role in Laotian history.

A microwave imagery pass over 99W earlier today indicated that there was a closed 20171230 0050 99W ASCATcirculation, albeit elongated.  Winds across the depression were generally around 30-35 km/h with pockets up to 45 km/h in thunderstorms displaced well to the northeast of center.  At 0900 UTC, the pressure in Koror, Palau was down to 1007.2 hPa, providing some support to JMA’s analysis of the depression.  Interestingly, the 0600 UTC analysis from JTWC indicated the winds were 30 km/h with a pressure of 1010 hPa–both values too weak when compared to observed data.  None of the major agencies are issues Dvorak analyses at this time.

Forecast guidance is continuing to come in better agreement, strengthening the confidence in the forecast.  All the major global models have backed off on intensity, keeping 99W as a tropical depression or possibly a very weak tropical storm.  Given that the depression is already over Palau, the window of opportunity to strengthen is beginning to close.

No significant deviations to the forecast track as 99W is expected to continue moving toward the west or slightly north of west through landfall, south of the trailed end of a cold front passing through the Philippine Sea.  With this track, CARAGA region is expected to receive the center landfall.  However, with heavy rainfall being the main threat from this system, all interests within the Visayas and Mindanao should continue monitoring the progress of this tropical depression.  Computer projections indicate that the eastern Visayas and northern Mindanao may see rainfall totals of 100-200 mm per day, further hampering recovery efforts from Vinta.

Mike Adcock
Meteorologist, Western Pacific Weather

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