When a storm approaches, the number everyone repeats is the signal. Signal No. 3 sounds serious, Signal No. 1 sounds survivable. But the wind signal answers only one question, and it is probably not the question that decides whether your house floods.

What a wind signal actually measures

Tropical cyclone wind signals are about wind, and only wind. PAGASA raises them to warn an area about expected wind speed within a stated lead time. Since the system was updated in March 2022, there are five levels:

• Signal No. 1. Winds of 39 to 61 kilometers per hour expected. Minimal to minor threat.
• Signal No. 2. Winds of 62 to 88 kilometers per hour. Minor to moderate threat.
• Signal No. 3. Winds of 89 to 117 kilometers per hour.
• Signal No. 4. Winds of 118 to 184 kilometers per hour. Significant to severe threat.
• Signal No. 5. Winds of 185 kilometers per hour or higher. Extreme threat.

The higher the number, the stronger the wind and the shorter the warning time, because a stronger, closer storm leaves less room to prepare.

That is the whole scope. It is a wind forecast for an area. It says nothing about how much rain will fall, and nothing about where that rain will go.

Why a low signal can still flood you

Some of the worst flooding in Philippine memory happened under low signals or no signal at all. A storm sitting offshore can pull in the southwest monsoon and dump enormous rain on land it never touches. A slow tropical depression can drop more water on a province than a fast typhoon does, because it lingers.

So the signal and the flooding come apart regularly:

• A weak system that stalls can produce days of rain under Signal No. 1.
• A strong typhoon that crosses quickly can raise Signal No. 3 and leave less rainfall behind than the slow one did.
• A storm outside the country entirely can still soak Luzon by enhancing the habagat.

If you take one thing from this: do not read the wind signal as a flood forecast. For rain, watch the separate color-coded rainfall warnings, which we covered in what a PAGASA rainfall warning means for your exact address.

Three different warnings, three different questions

It helps to keep the systems straight, because they are genuinely separate and they are issued separately:

1. Wind signal (1 to 5). How hard will the wind blow here? Matters for roofs, windows, trees, power lines, and whether it is safe to travel.
2. Rainfall warning (yellow, orange, red). How hard is it raining right now? Matters for flooding, in the next few hours.
3. Storm surge advisory. How far will the sea come inland? Matters only for coastal areas, and it is measured on its own scale. We explain that one in storm surge advisory levels explained.

A coastal town can be under a modest wind signal and a serious surge advisory at the same time. An inland town can be under a high wind signal with no surge concern whatsoever. Reading only the signal number collapses three questions into one, and loses the two that usually cause the damage.

The question none of the three answers

All three warnings describe the storm. None of them describes your ground.

That is the gap. PAGASA can tell an entire province that 100 millimeters of rain is coming. It cannot tell you whether your particular lot is four meters above sea level next to a creek, or thirty meters up on a plateau. Those two addresses will have completely different days under the identical warning.

The ground answer is made of things that do not change between storms:

• Elevation and slope, which decide whether water gathers or leaves. See elevation and slope.
• Distance to the nearest river, creek, or canal.
• Whether the lot sits inside a modeled flood or storm surge zone, and how frequent the storm has to be to reach it.

You can find all of that out on a clear day. That is the advantage: the storm warning is urgent and temporary, the ground profile is calm and permanent, and knowing the second makes the first actionable instead of just alarming.

A practical way to use all of it

1. Learn your ground profile once, when no storm is coming.
2. Write down what each warning means for you specifically. Not "orange means flooding possible" but "orange means I move the car, because we are in a frequent flood zone."
3. Watch the rainfall warning during the event, not the wind signal, if flooding is your main concern.
4. Watch the wind signal for structural and travel decisions: whether to board up, whether to drive, whether to expect a power cut.
5. If you are coastal, treat the surge advisory as its own thing and do not let a low wind signal talk you out of it.
6. Know your exit route in advance, and know whether the road out is exposed.

The honest limits

A hazard screening is not a forecast and never will be. It cannot tell you a storm is coming, how strong it will be, or when. PAGASA does that, and during an actual event their bulletins are the authority, full stop.

What a screening does is answer the question the bulletins structurally cannot: given water arriving here, what happens? It is a screening built from national datasets, so it reads the landscape rather than your specific lot, and it does not know about a blocked canal or a neighbor who raised their ground last year. Used together, though, the two fit neatly. One tells you what is coming. The other tells you what it means where you live.

CheckHazard does not replace a professional geotechnical or engineering survey.