NAM surface temperatures (top) and surface winds (bottom) showing development of onshore flow by afternoon.

First and foremost, welcome to Meteorological Autumn. The meteorological calendar officially flipped seasons from Summer to Autumn this morning at 12:00am, just as September began throughout the nation. Meteorological Autumn comes a full 21 days before the official calendar Autumn begins later this month. Taking a step back, though, and checking out some statistics from August, will leave you with answers to some questions. Why did the month seem cooler than usual? August averaged average to 2 degrees above average throughout the area, down several degrees from July. Why did the flooding seem so bad and so widespread this past week? Our area recieved over 18 inches of rainfall just in the month of August, a new *all time* record for New York City. Luckily, for the near future,  heavy precipitation is not in the forecast. Thursday looks to be characterized by a fairly routine occurrence in transition seasons (Autumn and Spring) in this area, which is the presence of a back door cold front and the development of a sea breeze near the shore. This is not to say that the day is a wash out totally, but the presence of the back door cold front will definitely be intrusive by afternoon.

Today (Thursday): Partly sunny, t shirt weather early on, and good beach weather for the first few hours of the day into the early afternoon. Winds then turn southeast and a back door cold front allows for sea breeze development near the coast. Overnight may require a long sleeved shirt, at the shore as well with some clouds and possibly a stray shower.

Tonight (Thursday Night): Cool again over the interior, with temperatures forecast to drop into the 50's. Clouds may stick around for some of the evening, but it won't be completely overcast. We recommend a long sleeved shirt in most spots, or maybe even a sweatshirt near the shore with east winds off the water.

Beware of the back door: Many websites and weather outlets will mention a back door cold front throughout the year in relation to our sensible weather here in New York, but not many take the time to explain it. Fortunately, it's not all that complicated. The name "back door" comes from the fact that the front is essentially coming in the opposite direction as it typically does (from the west, or northwest). Back door cold fronts move in from the east and northeast and are related to areas of troughiness over the Atlantic Ocean. As they move through, they switch surface winds from south or southwest, to east or southeast, bringing in air off the cooler waters, and often bringing in clouds, showers, and increased humidity. Although today's back door cold front is not very strong, it will still keep temperatures lower near the shore and bring some clouds there as well (see the above image and the big temperature gradient from the shore to inland areas).

Forecast model tracks for Katia, showing a good chance of a re-curve over open water.

Katia Update: Hurricane Katia officially formed in the Eastern Atlantic Ocean at 11:00pm on Wednesday Night, becoming the second named hurricane of the Atlantic Basin 2011 hurricane season. Katia now has sustained winds of 75 miles per hour, making her a weak Category 1 Hurricane. Strengthening is forecast by almost all global models throughout the next few days as she continues moving to the west-northwest, and some models have Katia reaching major hurricane strength by this weekend. Luckily, Katia looks to have multiple chances to be picked up by upper air troughs (with cold fronts) over the Eastern US by the time it gets closer to our area. Historically, storms that form in Katia's position and move on her heading have a less than 25 percent chance of making landfall on United States soil. We will certainly keep an eye on her, though!

Article written September 1st, 2011 at 12:02am. Looking for a forecast? See New York Metro Weather's Long Range Forecast for the rest of the week, or view our Technical Forecast Discussion for the more serious weather enthusiasts. Also, check out our new Forecast Overview tab. For up to the minute details on forecasts, watches, warnings, and alerts, follow us on Twitter and Facebook.