Historical weather data, all-time temperature records, and monthly climate averages for Iselin, NJ. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 4 in Iselin sits right in that shoulder-season sweet spot — expect a high near 58° and a low around 39°, though the date has swung wildly from 79° back in 1981 to a bitter 26° in 1995. There's a coin-flip chance of rain (54%), so keep a jacket handy, but snow is off the table entirely.
Iselin's weather has real range — 57 years of data capture everything from a scorching 105° on July 7, 2010 to a bone-chilling -13° on January 22, 1984, a spread of 118 degrees. The wettest single day on record dumped nearly 8 inches of rain (7.96") on August 28, 2011, courtesy of Hurricane Irene, and a February 2006 snowstorm dropped 19.8" in a single day.
Iselin peaks in summer, with the warmest stretch running mid-to-late July when average highs hit 88° — but that's also when rainfall is heaviest, averaging 1.39" in a single week in late July. Winters are cold but not brutal, with January highs averaging just 39°. Spring and fall offer the most comfortable windows, with May and September both delivering mild temperatures in the low-to-upper 70s.