September: a month of transition

September in Minnesota is usually a month of rapid transition from the heat, bouts of humidity and rounds of thunderstorms to cooler and much drier weather. "Crisp" often can be used to describe morning temperatures, especially later in the month.

This year the autumnal transition began on Labor Day after a cold front broke the back of what had been an abnormally muggy week. Dew points today have fallen into the very comfortable 40s and even 30s with some 50s and low 60s lingering in southern Minnesota.

The next chance of scattered showers and a few thunderstorms will come our way from the west starting late Wednesday into Thursday.

A cold front with Canadian air behind it will clear the state on Thursday to bring in slightly cooler air and reinforce the low dew points.

Tropical storms and hurricanes

While we are exiting our severe weather season, the tropical storm belts often are hitting their full stride. Although the official Atlantic hurricane season runs from June 1 to November 30, tropical storms and hurricanes are most common from mid August through late September.

Tracks of these storms follow a general historical pattern, but individual storms can be highly erratic. It is easy to forget that devastating Hurricane Katrina, ten years ago, first struck the Bahamas as a tropical storm and then made a left turn to hit Florida as a Category 1 hurricane. Katrina continued across Florida and out into the Gulf of Mexico where it became a Category 5 monster that put New Orleans in its sights.

This map shows all the known hurricane tracks for the Atlantic Basin since 1851 and the eastern Pacific since 1949.

This fall there is a new observational platform to assist in tropical storm forecasting. NASA's Global Hawk drone will be based at NASA's Wallops Flight Facility in eastern Virginia through the end of September. Its mission is similar to that of hurricane hunter aircraft: collect weather data over the ocean for input into the tropical forecasting models. Advantages it has over the aircraft are that it can operate up to 60,000 feet — 20,000 feet higher than the aircraft — and its mission can last for 24 hours.

Northern lights?

One unrelated additional note: Northern lights were spotted in Europe and across portions of the northern U.S. last night. The solar wind continues to impact Earth, so the aurora might return tonight. Skies will be dark as the moon is only a crescent and will not rise until after 3 a.m., so any northern lights would be especially visible.