Sun Sep 25 & Mon Sep 26 Outlook

Trailing cold front produces showers and thunder for NE late Sunday; keeping an eye on waivers related to Ian.

Welcome to any new readers! And as a reminder to long-ish time readers, we’re testing a new format for these outlooks. To both old and new—we’re grateful you’re here.

If you have questions about the content of this outlook, the answers might be in this post (we keep adding to it). Otherwise, let us know if something doesn’t make sense (we welcome feedback of all kinds!).

---

Sunday, September 25

We forecast TSA will screen 2.360 million travelers (± 0.5σ, or a prediction interval of about 38%, is 2.30-2.42 million travelers).

A low pressure system over the Great Lakes swings a warm front through the Northeast Sunday morning before sending a cold front through the region late Sunday. A few showers are possible with the warm frontal passage in the morning; behind the warm front, a moist southwest flow will make for an at least somewhat unstable air mass. A second round of showers—this one with a chance for thunder—is expected during afternoon and evening ahead of the cold frontal passage. While the mention of strong to perhaps severe thunderstorms is omitted from the New York forecast discussion, NWS Baltimore/Washington does carry it.

The trailing cold front stretches to North Texas, though pre-frontal moisture is meager around DFW and thus any convection should be pretty isolated.

Monday, September 26

We forecast TSA will screen 2.312 million travelers (± 0.5σ, or a prediction interval of about 38%, is 2.25-2.37 million travelers).

Though much of the day should be dry for NYC, can’t rule out a shower given the weak low pressure passing to the north.

With our new twice-weekly cadence, we won’t be publishing again until Wednesday. In the interim, we’ll be keeping an eye on Tropical Storm Ian (fka tropical depression 9), whose outer rain bands could reach South Florida late Monday. While there’s ample uncertainty, Ian is forecast to approach the Florida Peninsula¹ early- to mid-week at or near major hurricane strength. American, Delta, and United all have a waiver out that covers Grand Cayman (GCM) and some surrounding Caribbean airports—watch for these to be expanded to major airports in Florida.

You can check out hourly² estimates in this workbook.

1. Source: National Hurricane Center

2. While it links to a Google Sheet, it’s an Excel file and relies on the XLOOKUP function, which does not exist in Sheets. You can download the file and open in Excel, which should resolve the #NAME? error; if any readers don’t have Excel, let us know and we can work on a solution.