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September 2025 OBS-Discussion centered NYC subforum


wdrag
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Additional rain is likely tonight into tomorrow. A storm total 0.50"-1.50" rainfall covering late yesterday through tomorrow is likely in New York City and nearby suburbs. Some locations could see higher amounts in excess of 2.00". The potential for an area of 1.00"-3.00" rainfall exists for parts of Connecticut, Massachusetts, and a secton of southeastern New York State well north and west of New York City.

Above normal temperatures will continue through at least the coming weekend. Another round of showers is possible Saturday night into Sunday.

In addition, Humberto has developed in the central Atlantic and a second tropical cyclone could develop in the western Atlantic in coming days. The extent of ridging to the north and interaction between the two systems could ultimately determine whether one of these systems poses an eventual threat to a portion of the Southeast or stays out to sea.

The potential Fujiwhara interaction would be unusual for the Atlantic basin. Typically, if the stronger system is to the right or east of the weaker one (possibly Invest. 94 as per most of the guidance at present), the stronger system will tend to deflect the weaker one northward and eastward sooner than might otherwise be the case. If both systems are of similar strength, they can rotate counterclockwise around a midpoint roughly between the centers of the two storms as they move along the steering flow. 

For now, tropics bear watching. 

The ENSO Region 1+2 anomaly was 0.0°C and the Region 3.4 anomaly was -0.4°C for the week centered around September 17. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.03°C and the ENSO Region 3.4 anomaly has averaged -0.38°C. La Niña conditions will likely develop during mid- or late-autumn.

The SOI was +1.43 today. 

The preliminary Arctic Oscillation (AO) was +1.113 today. 

Based on sensitivity analysis applied to the latest guidance, there is an implied near 82% probability that New York City will have a warmer than normal September (1991-2020 normal). September will likely finish with a mean temperature near 70.0° (0.8° above normal). 

Supplemental Information: The projected mean would be 2.0° above the 1981-2010 normal monthly value.

 

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4 minutes ago, Brian5671 said:

HRRR keeps the northern extent going

Major improvement on the 20z HRRR compared to 19z. Still weakens it though, but 19z fizzled it out everywhere. 

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