As forecast here back on August 24th, September was looking to be a warmer and better month for the very areas which suffered a cool and wet summer. For particularly the Central and Northern Plains, Great Lakes and Ontario, it’s been a downright hot and pretty dry September.

The areas which saw more warmth and dryness June-August saw opposite with cooler and wetter including the Southeast and Pacific Northwest. It’s been another unexciting month for heat and more noted for wet in the Southwest once again.

This is a textbook example of how the same drivers have differing influence at different times of the season.

September temperature departure up till now.

I think you’d agree that we’ve seen a bookend summer with warm, dry end to spring (May) over the Plains, Great Lakes, Ohio Valley and Northeast and now this has repeated for Fall’s opening month. Not unknown during El Nino years.

How’s October Looking?

As for October, the pattern is looking similar with cooler and wetter around the coasts which are surrounded by warmer than normal water, whereas it’s drier beneath a sprawling strong than normal high pressure system. The MJO (Madden Julian Oscillation) appears to be favouring warm phases 6 through 8 for October.

The strong, more northerly positioned high which dominated September looks likely to hold through the first half of October. We’re watching the behaviour of tropical cyclone movement over the western Pacific as this has significant and direct influence downwind over North America. Modelling shows troughs continuing to dig down the West Coast bringing cooler, wetter but this pumps the ridge, warmth and dryness northward through the Plains, Midwest and East but a recurving west Pacific typhoon would support more of an Eastern US trough and I think that’s more likely through the second half of October.

A Very Real Tropical Threat

The tropical threat is becoming increasingly real as we enter October as water reach their peak heat potential and with strongest upper heights up across the Northern Tier, lowering heights over abnormally warm waters signals trouble.

The door to a very real tropical threat with widespread below normal heights extending from Caribbean into the Gulf Coast as well as the Atlantic Seaboard. Waters remain in the balmy 85-90 degree range just offshore and this setup is classic for October hits during El Nino years.

Current SSTA’s (Sea surface temperatures)

CFSv2 500mb height anomaly for October

2 metre temperature anomaly

Precipitation anomaly

CFSv2 weekly breakdown

500mb height anomaly

CFSv2 weekly 2 metre temperature anomaly

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