JACKSONVILLE, Fla. -- The arrival of cooler-than-normal temperatures in September and early October brought fall-like weather much earlier than usual this year.

Jacksonville's senior meteorologist not only prepares his daily forecasts and monthly garden tips, but also puts some broader thoughts together for a regular column here on News4Jax.com.

This was the coolest summer in 19 years with an average temperature of 79.1 degrees, which is 1.6 degrees cooler than normal. The number of 90-degree days was down to only 48 this year, 29 fewer days than the total of 77 days in 2000.

The seasonal winter monsoon, a buildup of cold air and high pressure over the northern hemisphere of Asia and North America, has already developed. Invasions of polar air will increasingly cause tropical rains to retreat farther south as we move into our dry season. November is normally our driest month of the year with an average rainfall of only 2 inches.

The arrival of cooler weather accompanied by the southward dip in the jet stream is beneficial in two ways. First, it causes late-season Atlantic and Caribbean tropical storms to turn eastward before reaching northern Florida. Our only threat would be from a storm in the Gulf of Mexico. Second, the cooler temperatures reduce growth of our plants and vegetation, making them less vulnerable to freezing temperatures.

Our average first freeze is between Nov. 29 and Dec. 4. Our earliest freeze was on Nov. 3, 1954, when the temperature dropped to 29 degrees. The probability of freezing temperatures increases from 10 percent on Nov. 14 to 30 percent on Nov. 21. The chance of a freeze occurring by Dec. 1 is 50 percent.

One benefit of an early freeze is the reduction of mosquitoes. In 1888, a killing frost on Nov. 25 brought an end to Jacksonville's yellow fever epidemic. About 5,000 residents were stricken with the disease, 400 of whom died.

A study of our climate patterns by the National Climate Prediction Center shows that there is no predictable pattern to show how cold our winter will be. If the dip (trough) in the jet stream pattern over the eastern U.S. as seen in mid-October persists into mid-winter, we may see our coldest winter in years. But, in most years, the jet stream pattern doesn't remain the same more than a month or two.

We'll keep you posted on the latest patterns on Eyewitness News.