Warmth and humidity to return again as anomalous ridge develops

If you were thinking that we had seen the last of warmth and humidity this year, think again. Forecast model guidance is in excellent agreement that a large ridge will develop across the Central and Eastern United States in the next 5 days. This will lead to the development of anomalously warm conditions from the Plains to the East Coast.

In the Northeast, temperatures could average several degrees above normal for more than a week. At times, forecast model guidance suggests that temperatures could average 15 to 20 degrees above average. Those kind of numbers will lead to unusual – and likely uncomfortable – warmth and humidity.

A summer-like ridge expected to form

Large and sprawling ridges of high pressure have developed across the Central and Eastern United States a few times already this Summer – and multiple times in the past few weeks. This one, though, looks to be particularly strong. Guidance suggests that heights in the mid levels of the atmosphere could approach summer-like levels during the week ahead.

When large ridges of high pressure like this develop, the airmass and air flow can quickly lead to abnormal warmth. Temperatures across the Central United States, particularly from the Plains toward the Ohio Valley, are likely to average 10 or more degrees above normal in the next week.

This warmth will eventually make it into the Eastern United States as well, with temperatures skyrocketing well above normal as we move through the last several days of September. There are some signals that this warmth could continue into the early part of October as well.

Here in New York City, this type of atmospheric pattern almost always means two things: Warmth and humidity. Dew points will gradually rise, and as the airmass around us modifies and the ridge remains in place, temperatures will eventually reach several degrees above normal, too. The forecast during the week ahead is likely to feature temperatures warming into the 80’s by the weeks end.

Tropics expected to remain active

Medium range weather model guidance is also in excellent agreement that conditions will remain favorable for tropical development in the Atlantic over the next 10-14 days. Tropical Storm Karen recently formed and is expected to pass near Puerto Rico before moving northward – but the systems path after that time also remains an uncertainty.

Additional tropical cyclone development is anticipated with clusters of thunderstorms emerging off of Africa in the next week. Multiple systems could develop and begin a general westward movement through the Tropical Atlantic.