Coastal flooding will always be a concern, and that concern has steadily increased in recent decades.
Compared with the 1950s and ’60s, the 2010s have seen about eight times more coastal flooding events annually.
In 2030, three months of the year would have coastal flooding, according to the Union of Concerned Scientists.
“Each year we settle (or sink) a little more. For people who don’t want to live by the ocean, then living inland is the only solution, but no matter what, wherever you live you have issues. You just need to be aware of your surroundings and be prepared,” said Donna Peterson, emergency management coordinator for Ventnor.
Since 1978, the Federal Emergency Management Agency has paid out more than $1.1 billion for losses along the South Jersey barrier islands and Delaware Bay communities due to flooding.
With coastal flooding occurring with such frequency, and at such a high cost, it is important to know the five factors that come into play: wind direction, wind distance, wind speed, duration of onshore winds and moon phase.
Any onshore wind will push waters from the Atlantic Ocean onto the shores, back bays and the Delaware Bay, that includes a southerly wind, since South Jersey is shaped south-southwest to north-northeast.
“A southeast wind favors the waters building up in the Chesapeake and Delaware bays. Our biggest surges during the winter are from east-northeast, which is worst for heavy wave action on the south side of inlets,” said Jim Eberwine, retired National Weather Service forecaster.
The longer the distance of onshore winds, the more water that can be carried onto shore. Weather systems that have onshore winds for 1,000 miles will carry more water, and bring more water to the shore, than one for just 100 miles. When talking about a low-pressure system, an “elongated” trough, or an area of low pressure shaped like an oval, will generally produce some of the worst coastal flooding.
Eberwine said that when the low pressure isn’t nearby, an origin farther east than Cape Cod will produce coastal flooding.
The stronger the onshore winds, the more ferociously the water will push onshore. Weak winds will likely not bring much coastal flooding, unless they run for long periods of time.
Sometimes, coastal flooding lasts for just one high-tide cycle. Other times, it is an issue for days. Days of onshore winds will “stack” the water, not allowing it to effectively drain out during low tides. The back bays are the most susceptible to stacking.
“Our main problem in Ventnor with the coastal flooding is being cut off and the subdivision (Inside Thorofare) within the city itself. Once the flooding starts, if you are in Ventnor Heights you will have no access because Wellington Avenue and Dorset Avenue will be flooding and impassable,” Peterson said.
Even after the winds turn to an offshore direction (westerly, northerly are examples), a stacking situation may require strong winds to end the flooding threat.
Days of the full and new moon, and the one to two days surrounding it, will also bring higher tides.
When the moon is full, it is on the opposite side of the Earth from the sun, and the gravitational pull of the moon and sun are combined. During these times, the high tides are very high and the low tides are very low.
During the quarter moons, the pull from the moon and sun negate each other, so the tides are not as extreme.
Peterson said three days before a coastal flood, her city’s emergency management officials start monitoring and getting prepared, in part because she knows what the moon phases will be like well in advance.
“We send out notifications for what might happen and set out barricades for certain areas that flood so cars will not drive through those areas. The day before we verify the information we have for tides and weather and send out the appropriate notifications via our social media,” she said.
As if predicting storms isn’t tricky enough, there are other variables: all five factors aren’t required for coastal flooding; and sometimes those same factors won’t lead to flooding.