The weather has been streaky that way for many moons. Frequent and/or long lasting storms punctuated by glorious weather. Lately the glorious mode has been dominant.
And the reason for the Delaware’s long descent to somewhat below normal is the more sudden crash of many of the Pennsylvania tributaries like the Broadhead Creek, which is a few hundred cfs below the median. That’s the result of the unseasonably hot, dry windy weather we enjoyed.
The mighty Lehigh too is well below normal, a full 1000 cfs below at Bethlehem.
On the Jersey side of the river, tributaries like the Flatbrook and Musconetcong River are near or slightly below the median.
The difference between the overall flow of the two states' tributaries is expressed in the rainfall distribution from the last nor’easter, which hammered the coast with up to 15 inches in some places, but only gave the Poconos and westernmost PA piedmont a paltry few inches by comparison.
And that’s the way it is. And as usual, changes are on the way.