MANILA, September 4, 2026 — Millions of Filipinos across Luzon and Visayas are waking up to another rain-soaked day as the southwest monsoon, or "habagat," continues to push widespread and sometimes heavy rainfall across the country. The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) issued its 4:00 AM forecast on Thursday, September 4, valid until 4:00 AM on Friday, September 5, warning of flash flooding and landslide risks in several provinces.
A tropical depression is also being tracked outside the Philippine Area of Responsibility (PAR), located approximately 1,770 kilometers east of extreme Northern Luzon, packing maximum sustained winds of up to 65 kilometers per hour near its center and gustiness of up to 80 kph. It is moving northwestward at 10 kilometers per hour. While currently outside PAR, PAGASA is monitoring its movement closely.
What Is Driving Today's Weather
The dominant force shaping the day's weather is the southwest monsoon, commonly known in the Philippines as "habagat." This is a seasonal pattern in which warm, moisture-laden winds blow from the southwest — sweeping in from the sea — and pile up against Luzon and the Visayas, releasing large amounts of rain. It is the country's main rain-producer during the June-to-October wet season, and when it is active and enhanced, as it is today, it can sustain hours of rainfall and trigger flooding in low-lying areas and landslides in mountainous terrain.
PAGASA notes that the tropical depression now east of the country, while still outside PAR, may be contributing additional moisture to the monsoon flow — a common dynamic during the wet season that can intensify habagat rains even without a storm making landfall.
Region-by-Region Forecast
Northern Luzon
Zambales and Bataan bear the brunt of the monsoon today, with PAGASA flagging possible flash floods in both provinces. Residents in low-lying and near-river communities in these areas should remain on alert. Coastal waters off Northern Luzon are forecast to be rough to very rough, with wave heights that make sea travel dangerous for all types of watercraft.
Metro Manila and Central Luzon
Metro Manila, Pangasinan, Pampanga, Tarlac, Bulacan, Cavite, Laguna, and Occidental Mindoro can expect scattered rainshowers and thunderstorms throughout the day, driven by the southwest monsoon. Flash flooding remains a concern in low-lying urban areas — particularly in Metro Manila where drainage systems can be quickly overwhelmed during intense downpours. Residents in flood-prone barangays should monitor local government advisories closely.
The Rest of Luzon and CALABARZON/MIMAROPA
The rest of Luzon — encompassing CALABARZON, the MIMAROPA region, and their surrounding areas — faces moderate to heavy rain with the elevated risks of both flash floods and landslides during severe thunderstorm episodes. Communities on hillsides or near rivers and drainage channels are at heightened risk. PAGASA specifically notes that landslide threats are present in these areas today.
Visayas
The Visayas is also under the influence of the southwest monsoon today. The forecast calls for rainshowers and thunderstorms with potential for flash flooding and landslides during the more severe rain episodes. Coastal waters across the Visayas are described as moderate to rough, posing risks for smaller fishing vessels and passenger boats. Residents in eastern Visayas, in particular, should note that conditions may be changeable throughout the day.
Mindanao
Mindanao is experiencing more localized weather today, with PAGASA forecasting isolated to scattered rainshowers and thunderstorms. Flash flooding and landslides remain possible during the more intense storm episodes. Coastal waters in Mindanao are generally slight to moderate, meaning conditions are comparatively calmer, though small boat operators should still exercise standard caution. The rest of the country's coastal waters are forecast to have wave heights of 0.6 to 2.1 meters under light to moderate southwest winds.
Decoding the Warnings: What Each Means for You
PAGASA's forecast today does not include any tropical cyclone wind signal — the tropical depression is still far outside the country's boundaries. However, the agency's weather descriptions carry important implied risk levels that every Filipino should understand.
The terms "rough" and "very rough" seas in Northern Luzon are formal PAGASA coastal water classifications. Rough seas mean that wave heights and wind conditions are already dangerous for small fishing boats and bancas. Very rough conditions extend that danger to larger vessels. When PAGASA uses these terms, fisherfolk and ferry operators should treat them as a direct instruction to stay in port.
Similarly, when PAGASA warns of "possible flash floods" and "landslides," these are not remote possibilities — they are conditions that the forecast models show are plausible given the projected rainfall intensity. Communities in identified risk areas should have evacuation plans ready and should not wait for the flooding or land movement to begin before acting.
For a full explanation of all PAGASA warning levels — including rainfall color codes (yellow, orange, red), tropical cyclone wind signals (No. 1 to 5), and heat index categories — see our guide on how to read PAGASA's weather warnings.
What It Means for You
Commuters
Expect rain throughout much of the day in Metro Manila and across Central Luzon. Flash floods can develop quickly in low-lying streets and underpasses during intense downpours. Avoid flooded roads and do not attempt to cross running water on foot or by vehicle. Add extra travel time and check local government announcements on road closures before leaving home.
Fisherfolk and Small-Boat Operators
Conditions in Northern Luzon's coastal waters are rough to very rough today — PAGASA's forecast is a clear signal to remain ashore. Even in the Visayas, where seas are moderate to rough, small bancas and fishing boats are at risk. Only those with larger, properly equipped vessels should consider going out, and only after verifying current sea conditions with local coast guard stations.
Farmers
While monsoon rains are welcome for many crops, sustained or heavy downpours increase the risk of soil erosion, crop damage from flooding, and post-harvest losses for any crops already cut and drying. Farmers in Zambales, Bataan, Central Luzon, and the Visayas should secure harvested produce and avoid fieldwork in areas prone to waterlogging or runoff today.
Students, Parents, and School Administrators
Classes in areas under heavy rain warnings — particularly those in Zambales, Bataan, Metro Manila, and Central Luzon — may be disrupted by local government suspension orders. Parents should monitor announcements from their local city or municipality and from the Department of Education before sending children to school. Do not allow children to wade through flooded streets.
Outdoor Workers and Construction Sites
Workers in outdoor and construction roles across Luzon and the Visayas face heightened risk today from sudden intense rainfall, lightning during thunderstorms, and flash flooding. Employers and site supervisors should assess conditions before the workday begins and have a clear plan for safely suspending outdoor work during severe thunderstorm episodes.
Temperature and Humidity Outlook
PAGASA's forecast includes temperature readings for Metro Manila, with a minimum of 27°C recorded at 5:00 AM. Relative humidity in the city reaches a minimum of 74% at 2:00 PM, reflecting the sticky, muggy conditions typical of the monsoon season. Maximum temperature in Manila is recorded at 30.5°C. These figures underscore that even on a rainy day, the humidity can make conditions feel uncomfortable — particularly for outdoor workers and those without air conditioning.
Astronomical Information
PAGASA notes that the moon is at 40% illumination today. Tidal information is available through NAMRIA. Sunrise and sunset times, as well as moonrise and moonset data, are included in the full PAGASA bulletin for maritime and agricultural planning purposes.
Bottom Line
Bottom line: The southwest monsoon is bringing a genuinely dangerous rain day to much of Luzon and the Visayas on September 4. If you live in a flood-prone or landslide-prone area — particularly in Zambales, Bataan, Metro Manila, Central Luzon, CALABARZON, MIMAROPA, or the Visayas — do not wait for conditions to worsen before taking precautions. Fisherfolk in Northern Luzon should stay onshore. Everyone else should stay informed, keep emergency contacts ready, and avoid unnecessary travel during heavy downpours.
Monitor official PAGASA updates at pagasa.dost.gov.ph.