Tropical cyclone watches and warnings

Hurricane Warning Hurricane conditions expected within 36 hours.

Hurricane Watch Hurricane conditions possible within 48 hours.

Tropical Storm Warning Tropical storm conditions expected within 36 hours.

Tropical Storm Watch Tropical storm conditions possible within 48 hours.

Signal #1 winds of 30–60 km/h (20-37 mph) are expected to occur within 36 hours

Signal #2 winds of 61–120 km/h (38–73 mph) are expected to occur within 24 hours

Signal #3 winds of 121–170 km/h, (74–105 mph) are expected to occur within 18 hours.

Signal #4 winds of 171–220 km/h, (106–137 mph) are expected to occur within 12 hours.

Signal #5 winds of at least 220 km/h, (137 mph) are expected to occur within 12 hours.

Cyclone Watch Cyclonic storm conditions possible within 72 hours.

Cyclone Alert Cyclonic storm conditions possible within 48 hours.

Cyclone Warning Cyclonic storm conditions expected within 24 hours.

Landfall Outlook Cyclonic storm conditions expected within 12 hours.

Tropical cyclone warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate preparation for the cyclone, including evacuation of vulnerable areas where necessary. It is important that interests throughout the area of an alert make preparations to protect life and property, and do not disregard it on the strength of the detailed forecast track. Tropical cyclones are not points, and forecasting their track remains an uncertain science.

In conjunction with the National Hurricane Center, the national meteorological and hydrological services of Central America, the northern Atlantic Ocean, and the northeastern Pacific Ocean east of the 140th meridian west, excluding mainland Africa and Europe, all issue tropical storm/hurricane watches and warnings. Tropical storm watches are issued when gale and storm force winds of between 34–63 knots (39–73 mph; 63–118 km/h) are possible, within 48 hours in a specified area in association with a tropical, subtropical or post-tropical cyclone. These watches are upgraded to tropical storm warnings, when gale and storm force winds become expected to occur somewhere in the warning area within 36 hours. Hurricane watches are issued when sustained winds of 64 knots (74 mph; 119 km/h) are possible, within 48 hours in a specified area in association with a tropical, subtropical or post-tropical cyclone. These warnings are upgraded to hurricane warnings, when hurricane-force winds become expected to occur somewhere in the warning area within 36 hours.

Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch and warnings are issued in advance of the anticipated onset of tropical-storm-force winds, rather than in advance of the anticipated onset of hurricane-force winds. At times a tropical storm warning and a hurricane watch can both be in effect due to uncertainties in the forecast. These watches and warnings are also issued by the Central Pacific Hurricane Center for the Hawaiian Islands and the Weather Forecast Office in Guam for parts of Micronesia but not for American Samoa due to an international agreement.

...
Wikipedia