Hurricane Warning or Tropical Storm Warning: What Changes

Direct answer: a watch means the conditions are possible in your area, typically within about 48 hours. A warning means they are expected, typically within about 36 hours. The word in front — hurricane or tropical storm — tells you which wind speeds are expected, not how dangerous the storm is to you. A tropical storm warning over your town and a hurricane warning over the next island is normal, and it is not a ranking of who should worry.

The four products, as a grid

Almost every tropical cyclone warning system in the world is built from two questions: how likely, and how strong. Cross them and you get four products.

• Tropical storm watch. Sustained winds of tropical storm force — roughly 63–118 km/h, 39–73 mph — are possible, generally within 48 hours.
• Tropical storm warning. Those winds are expected, generally within 36 hours.
• Hurricane watch. Sustained winds of hurricane force — 119 km/h, 74 mph and above — are possible, generally within 48 hours.
• Hurricane warning. Those winds are expected, generally within 36 hours.

The 48 and 36 hour figures are the standard used by the United States National Hurricane Center and its Pacific counterparts. Other agencies use similar lead times under different names. What matters is the shape: watch buys you preparation time, warning spends it.

Why the lead time is the point, not the wind speed

People read the escalation from watch to warning as the storm getting worse. Often it has not changed at all. What changed is the forecaster's confidence and the clock.

A warning is issued about 36 hours ahead for a specific reason: that is roughly the last moment at which ordinary preparation is still possible. Boarding windows, fuelling a car, moving a boat, filling water containers and driving somewhere safer all take longer than people estimate, and all of them get harder once the outer bands arrive. Winds do not wait for the centre. Conditions on the ground usually deteriorate many hours before the storm itself is close.

By the time the wind you were warned about is actually blowing, the window the warning was protecting has already closed.

Why your island got a different warning from the next one

As this was written, the National Weather Service in Honolulu had a hurricane warning up for parts of Kauai and a tropical storm warning for Oahu — two islands, roughly 100 km apart, under two different products at the same minute.

That is not indecision. Warnings are issued for defined zones, and the forecast wind field is not uniform. The strongest winds in a tropical cyclone sit in a band around the centre, not across the whole system, so a track passing closer to one island genuinely means hurricane-force wind is expected there and not next door.

Two things follow, and the second is the one people miss:

• A different warning for a neighbouring area is expected behaviour, not a mistake or a contradiction.
• The boundary is a forecast, and forecasts move. A zone under a tropical storm warning this morning can be upgraded this evening. Warnings are re-issued, usually every few hours. The version you read once is not the version that is in force now.

The word that gets people killed is only

“It is only a tropical storm warning” is the most dangerous sentence in this subject, and it is dangerous because of what these warnings do not describe.

Both products are about wind. Neither is a statement about water. In tropical cyclones, water — storm surge along the coast, and freshwater flooding from rainfall inland — has historically caused the large majority of deaths, and rainfall totals are only loosely related to a storm's wind category. A weakening system moving slowly can drop far more rain than a stronger one moving fast.

Agencies issue separate products for the water precisely because it does not track the wind: storm surge watches and warnings, and flash flood watches and warnings. A tropical storm warning with a flash flood warning underneath it is a more dangerous combination for most people than a hurricane warning alone.

If you take one thing from this page: read the wind warning for the wind, and go and look for the water products separately. They are not the same alert and they do not cover the same area.

What each one is actually asking you to do

• At a watch. Decide now, while deciding is cheap. Fuel, cash, medication, phone chargers, water. Know where you would go and how you would get there. Confirm who is checking on anyone who cannot move quickly. Nothing here is difficult; all of it becomes difficult later.
• At a warning. Finish and stop. Complete outdoor work while it is safe. If an evacuation order has been issued for your zone, leave — the warning is a weather statement, the evacuation order is an instruction, and they are separate things. If you are staying, assume you will lose power and mobile coverage, and that nobody can reach you during the worst of it.

Emergency services suspend rescue operations once winds reach a certain strength, because sending a crew out becomes a way to lose the crew. That is the practical meaning of a warning: for a period, you are on your own.

What these warnings do not tell you

• Nothing about your building. Two houses under the same warning face very different risk depending on construction, elevation and what is upwind.
• Nothing about duration. A slow storm holds a coastline under damaging wind and rain for a long time. The warning names the hazard, not the hours.
• Nothing about after. Most tropical cyclone injuries in wealthier countries happen during clean-up and restoration, not during the storm. The warning ends long before the danger does.

How this site fits

Tropical cyclone warnings shown here come from the national agencies that issue them, and we publish each one with its source and a link back to the original. We do not forecast, and we do not upgrade or downgrade anybody's warning. For the area you actually care about, the agency that issued it is the authority — not us, and not a weather app.

Related reading: what a hurricane category actually measures, why storm surge is the deadliest part, and what an evacuation order means.

Frequently asked questions

Is a hurricane warning worse than a tropical storm warning?

It means stronger wind is expected - hurricane force is 119 km/h (74 mph) and above, tropical storm force is roughly 63 to 118 km/h. It does not mean the tropical storm warning is safe. Most tropical cyclone deaths come from water rather than wind, and neither of these products describes the water.

How much warning does a hurricane warning give me?

Typically about 36 hours before the expected onset of hurricane-force winds. A watch is issued around 48 hours ahead. Those hours are the point of the product: they are roughly the last window in which ordinary preparation is still possible.

Why does the next town have a different warning from mine?

Warnings are issued for defined zones and the strongest winds sit in a band around the storm centre rather than across the whole system, so neighbouring areas genuinely expect different conditions. It is normal, not an error - and the boundary can move, so check whether your zone has been upgraded.

Does a tropical storm warning cover flooding?

No. Both hurricane and tropical storm warnings are wind products. Storm surge and flash flooding have their own separate watches and warnings, they cover different areas, and rainfall is only loosely related to a storm's wind category.

Sources

• NOAA National Hurricane Center - Watches and Warnings
• NOAA Central Pacific Hurricane Center
• US National Weather Service - Tropical Definitions

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