September 2025 OBS-Discussion centered NYC subforum

[bluewave]

Record 500 mb ridge to our north will keep the heaviest rains to our south this week.

 

 

[SnowDemon]

11 hours ago, SnoSki14 said:

Endless summer. GFS OP showing 90s late September lol

And the 6z this morning says what 90s? lol. 

[jm1220]

Yawn. But Sept is usually a yawn month here unless a hurricane is coming up. Amazing how this season is dead as a doorknob though. 

[bluewave]

Friday looks like the warmest day of this week with Euro and GFS showing 85-90° potential on a dry W to NW downslope flow.

 

 

[donsutherland1]

Some model guidance has periodically shown a 90° or above temperature for the New York City area after September 15th. The forecast AO-/PNA- combination has seen a disproportionate share of such events.

However, these are infrequent events, so a lot more would need to be seen before it is evident that such an event is likely.

90° or Above Highs after September 15th (1980-2024):

New York City-Central Park: 7 days
New York City-JFK Airport: 6 days
New York City-LaGuardia Airport: 12 days
Newark: 18 days

One would need to see consistent guidance on multiple models with good run-to-run consistency. A big caveat this September is the fact that the ECMWF/EPS has been running a strong warm bias in the 2-5-day range. Moreover, in the cases of New York City and Newark, 80% of the years that saw such late-season 90s had warmer first halves of September than will be the case in 2025. At LaGuardia, 78% of such years had warmer first halves of September. At JFK, that percentage was 83% of years.

The most prominent notable exception that followed a cooler first half of September was 2017, which occurred to a highly amplified pattern. 

Currently, a 2017-type pattern is not showing up on the ensembles. 

In sum, unless there are some fairly dramatic changes, a 90° or above high in the New York City area during the second half of September appears unlikely. Newark has the best shot on Friday, but could fall several degrees short.