MANILA, Philippines — A developing low-pressure area (LPA) east of the Philippines may bring heavy rainfall to parts of Luzon and the Visayas later this week as it interacts with a strengthening northeast monsoon, according to international forecast agencies and recent numerical weather model guidance.
The system—invest designated 93W—is currently located west of Guam and continues to move slowly northwest. The Japan Meteorological Agency (JMA) has classified the disturbance as a minor tropical depression, though it remains outside the Philippine Area of Responsibility and is not yet designated as an LPA by PAGASA.
Satellite imagery shows a broad area of convection wrapping around the western periphery of the disturbance. Forecasters note that while 93W is gradually organizing, its future intensity will be limited by a strong shear line extending from Okinawa to the South China Sea. The same shear line weakened Typhoon Verbena (known locally as Koto) earlier this week.
Monsoon Surge Expected to Steer System Southwest
Meteorologists expect a new cold surge from Siberia to push southward beginning Tuesday. As this northeasterly flow strengthens, the developing system east of the Philippines is likely to be forced southwestward, a track scenario shown consistently by both the ECMWF and GFS models.
This setup may cause the disturbance to “skew” along the shear line, stretching its convection and preventing the kind of core development typically associated with full tropical cyclones.
“This is not a classic typhoon structure,” forecasters said. “Strong wind shear and dry air spilling south from the continent will heavily influence the system’s organization.”
Most Significant Impacts May Be South of Luzon
Current projections show a possible landfall between December 4 and 6, most likely over the Bicol Region or Samar, if the system consolidates into a tropical depression or weak tropical storm. However, meteorologists caution that the heaviest rainfall may occur north of the center, along the active shear line.
Rainfall is expected to build along eastern Luzon, Bicol, and Eastern Visayas as the monsoon surge forces moisture southwestward. Northern Luzon may remain comparatively dry, though gusty winds from the monsoon surge are possible.
Five-day rainfall outlooks from ECMWF show potential for significant precipitation along southeastern Luzon and Eastern Visayas, with totals increasing late in the week as the system interacts with the shear line.
Naming Remains Uncertain
JMA is not expected to name the system unless it develops stronger tropical characteristics. PAGASA may classify the disturbance as a tropical depression or name it Wilma if it enters the Philippine Area of Responsibility and meets criteria for a tropical cyclone designation.
Other Systems Still Active in the Region
Verbena/Koto continues to weaken east of Vietnam, though it is still contributing to regional wind shear. Meanwhile, Cyclone Senyar—responsible for severe flooding in Malaysia and Thailand—has also begun to dissipate.
Complex and Evolving Weather Pattern
Meteorologists emphasize that the interaction between 93W, the northeast monsoon, and evolving shear lines creates a highly dynamic environment, making precise forecasting challenging several days in advance.
“It’s a complex setup,” forecasters said. “This is not simply a storm approaching the Philippines. It is a tropical disturbance interacting with cold monsoonal flow and an extensive shear line, all of which determine where rain will fall.”
PAGASA and international agencies are expected to issue updates as the disturbance moves closer to the country.