Just three weeks after the remnants of Tropical Storm Ida swamped northern and central New Jersey with torrents of rain, turning streets into raging rivers and killing 30 people, the National Weather Service has posted a flash flood watch across most of the state.
While no one is expecting a repeat of the Ida catastrophe, forecasters are concerned that some of the thunderstorms that develop on Thursday could move slowly and drop 2 to 3 inches of rain during a short time span.
That’s why the weather service has issued a flash flood watch in 12 counties.
So what does a watch mean? And should people take it seriously?
A flood warning or a flash flood warning is more urgent than a watch, so drivers and pedestrians should avoid flooded streets and move to higher ground if a warning is issued.National Weather Service
Flash flood watch vs. flash flood warning
First things, first. Just like a severe thunderstorm watch, a tornado watch or a winter storm watch, a flash flood watch is not as urgent as a flash flood warning. It basically puts drivers, homeowners and public safety officials on notice that conditions are favorable for heavy rain to fall within a few hours.
As a result, there’s a possibility that streets and highways in some towns and cities within the watch area could get quickly flooded.
Nick Carr, a meteorologist at the National Weather Service’s regional forecast office in New Jersey, says one simple way to understand the difference between a watch and a warning is by using a baking analogy.
“With a watch, you have the ingredients of a cake, but you don’t have a cake yet,” he said. “If there’s a flash flood warning, the cake is there” or quickly on the way.
The official definition of a flash flood warning says it is issued when “flash flooding is in progress, imminent, or highly likely.” As soon as the weather service sees high volumes of rain detected over a specific area on radar or receives reports of roads that are starting to take on water, the agency will typically issue a flash flood warning for that area.
A flood warning or a flash flood warning is more urgent than a watch, so drivers and pedestrians should avoid flooded streets and move to higher ground in areas where warnings are issued.National Weather Service
Because flash floods can occur so quickly and can be deadly — as we all saw in early September — a flash flood warning is actually one of the few weather alerts that will sometimes prompt a loud emergency warning alert on mobile phones and other wireless devices. (It basically depends on how severe or how widespread the flooding is.)
Other wireless emergency alerts include tornado warnings, blizzard warnings and — added more recently — severe thunderstorms that are considered highly destructive because of intense winds and very large hail.
“A flash flood is a sudden violent flood that can take from minutes to hours to develop,” the National Weather Service notes. “It is even possible to experience a flash flood in areas not immediately receiving rain,” because of heavy runoff from nearby storm drains and drainage basins.
Weather experts advise drivers to be aware of the danger of high water building up on roads.National Weather Service
Flood advisory vs. flood warning
The National Weather Service also has some other water-related alerts at its disposal, including flood advisories, flood warnings and areal flood warnings.
These typically pertain to rivers, streams, creeks and other waterways that can overflow and cause flooding on nearby roads or in nearby neighborhoods.
Similar to a watch, an advisory is not as urgent as a warning, because a warning means flooding is either imminent or already occurring.
Carr said there could be some confusion among the public about the different types of flood alerts, and the weather service is planning to fine-tune them. But an areal flood warning is usually issued in cases of minor flooding in low-lying areas that could be more prone to flooding than other areas.
But just like the other alerts, a warning is more urgent than an advisory or a watch, the weather service notes. So people should take them all seriously because they could result in a drowning or property damage.
Safety tips from the National Weather Service.National Weather Service
Safety tips
If a flood watch or flash flood watch is issued, the National Weather Service says you should be prepared for the possibility of flooding and closely monitor the latest weather alerts in your area.
If a warning is issued, and you are in a flood-prone area, “move immediately to high ground,” the weather service says.
If you are driving on a road that is covered with water, turn around and find a safer route. (You are probably familiar with this frequent reminder from the weather service: “Turn around, don’t drown.”)
“Getting people not to drive through flooded waters is the biggest thing we ask,” Carr said. “Driving on flooded roadways is one of our biggest (concerns), because that’s what causes the most problems.”
Safety tips from the National Weather Service.National Weather Service
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Len Melisurgo may be reached at [email protected].