Flash Flood and Flooding in New Jersey, April 9 to 10, 1998

Name: Flash Flood and Flooding in New Jersey, April 9 to 10, 1998
Start: 1998-04-09T07:00
End: 1998-04-10T22:45
Location: New Jersey

April 9 to 10, 1998 · NWS PHI · 12 events in 9 counties and zones

A low pressure system moved into the central Ohio River Valley the morning of the 9th. Its associated warm front extended east into the Delmarva Peninsula.

Where it happened

Every event with a place to put it; 12 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 12

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS PHI wrote it up.

A low pressure system moved into the central Ohio River Valley the morning of the 9th. Its associated warm front extended east into the Delmarva Peninsula. A second low pressure system developed along this boundary on the Delmarva Peninsula the evening of the 9th and moved rapidly offshore the morning of the 10th. Rain overspread New Jersey the morning of the 9th, but fell at its heaviest during the afternoon and evening of the 9th. Precipitation changed over to snow across the extreme northwest part of the state overnight on the 9th. Lighter precipitation fell into the morning of the 10th. Storm totals averaged between 1.5 and 2.5 inches (with some locally higher amounts) from Burlington and Ocean Counties north. Less rain fell farther south in the state with storm total amounts generally around an inch. The heavy rain in the central and northern part of the state caused minor flooding along a few creeks and rivers in Mercer, Morris and Somerset Counties as well as the usual urban and poor drainage flooding. In Mercer County, the Assunpink Creek at Trenton was above its 7 foot flood stage from 1 a.m. EDT through 5 a.m. EDT on the 10th. It crested at 7.15 feet at 230 a.m. EDT. Later that day in Somerset County, the Raritan River at Manville was above flood stage (12 feet) from 1030 a.m. EDT through 2 p.m. EDT. It crested at 12.25 feet at Noon EDT. Also in Somerset County, the Millstone River at Blackwells Mills was above its flood stage (9 feet) from 1130 a.m. EDT through 1145 p.m EDT on the 10th. It crested at 9.54 feet at 6 p.m. EDT. In Morris County, the Rockaway River below the Boonton Reservoir reached its 5 foot flood stage at 430 p.m. EDT on the 10th. It crested at 5.04 feet at 6 p.m. EDT on the 10th and was back within bankfull at 11 p.m. EDT that evening. Storm totals included 2.77 inches in White House Station (Hunterdon County), 2.62 inches in Hackettstown (Warren County), 2.61 inches in Stewartsville (Warren County), 2.48 inches in Red Bank (Monmouth County), 2.34 inches in Belvidere (Warren County), 2.29 inches in Wertsville (Hunterdon County), 2.28 inches in Washington's Crossing (Mercer County), 2.26 inches in Hamilton Square (Mercer County), 2.20 inches in New Brunswick (Middlesex County), 2.07 inches at the Mcguire AFB (Burlington County), 1.99 inches in Iselin (Middlesex County), 1.98 inches in Lambertville (Hunterdon County), 1.82 inches in Freehold (Monmouth County) and Harvey Cedars (Ocean County), 1.77 inches in Washington Township (Morris County), 1.71 inches in Mount Laurel (Burlington County), 1.67 inches in Long Valley (Morris County) and 1.61 inches in Mount Holly (Burlington County).

The radar

The Philadelphia radar (KDIX), 81 km away, was scanning. The volume nearest the first event began at 12:00 UTC.

Open the radar archive at this moment

Event by event

9 heavy rain, 2 flood, 1 flash flood. Local standard time, as filed.

Heavy Rain, Hunterdon

When: April 9, 7:00 AM EST to April 10, 6:00 AM EST
Where: Hunterdon County, Countywide
Coordinates: 40.567, -74.912 (the zone’s center; the record gives no point)

Heavy Rain, Morris

When: April 9, 7:00 AM EST to April 10, 7:00 AM EST
Where: Morris County, Countywide
Coordinates: 40.862, -74.544 (the zone’s center; the record gives no point)

Heavy Rain, Burlington

When: April 9, 8:00 AM EST to April 10, 7:00 AM EST
Where: Burlington County, Countywide
Coordinates: 39.878, -74.668 (the zone’s center; the record gives no point)

Heavy Rain, Mercer

When: April 9, 8:00 AM EST to April 10, 7:00 AM EST
Where: Mercer County, Countywide
Coordinates: 40.283, -74.702 (the zone’s center; the record gives no point)

Heavy Rain, Middlesex

When: April 9, 8:00 AM EST to April 10, 8:00 AM EST
Where: Middlesex County, Countywide
Coordinates: 40.440, -74.409 (the zone’s center; the record gives no point)

Heavy Rain, Monmouth

When: April 9, 8:00 AM EST to April 10, 8:00 AM EST
Where: Monmouth County, Countywide
Coordinates: 40.288, -74.158 (the zone’s center; the record gives no point)

Heavy Rain, Ocean

When: April 9, 8:00 AM EST to April 10, 8:00 AM EST
Where: Ocean County, Countywide
Coordinates: 39.866, -74.250 (the zone’s center; the record gives no point)

Heavy Rain, Somerset

When: April 9, 8:00 AM EST to April 10, 7:00 AM EST
Where: Somerset County, Countywide
Coordinates: 40.564, -74.616 (the zone’s center; the record gives no point)

Heavy Rain, Warren

When: April 9, 8:00 AM EST to April 10, 5:00 AM EST
Where: Warren County, Countywide
Coordinates: 40.857, -74.997 (the zone’s center; the record gives no point)

Flash Flood, Mercer

When: April 10, 12:00 AM EST to 4:00 AM EST
Where: Mercer County, Trenton
Coordinates: 40.283, -74.702 (the zone’s center; the record gives no point)

Flood, Somerset

When: April 10, 9:30 AM EST to 10:45 PM EST
Where: Somerset forecast zone
Coordinates: 40.564, -74.616 (the zone’s center; the record gives no point)

Flood, Morris

When: April 10, 3:30 PM EST to 10:00 PM EST
Where: Morris forecast zone
Coordinates: 40.862, -74.544 (the zone’s center; the record gives no point)

What these are

Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in New Jersey in 1998 Every state in 1998 This day in weather history Warnings in New Jersey, April 1998

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 5643475, 5643479, 5643474, 5643476, 5643477, 5643478, 5643480, 5643481, 5643482, 5643471, 5643473, 5643472.