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Latest weather and tropical outlook as of September 7, 2018

Have you been taking advantage of the glorious weather to harvest your grapes? We have seen better weather than I expected since my last weather update on August 24. The last two weeks have been much below normal in precipitation and temperatures have been running 2-4 degrees above normal during the same time period for most of Georgia and the surrounding states. The only exception to that is southwestern Georgia and points west, where Tropical Storm Gordon dropped heavy rain and brought cooler temperatures to that part of the Southeast. This lovely weather is due to the presence of a strong high pressure system which is parked over the Southeast, preventing the formation of all but the most widespread afternoon thunderstorms. This is a contrast to earlier in August, when daily rainfall was much more common. The high pressure is expected to stay over the area for the next few days but a cold front will gradually move into the area from the northwest, bringing more frequent but still scattered showers to the area by mid-week.

Longer term, the forecasts I have seen for the next several weeks indicate that above normal temperatures are likely to continue, with no big cold outbreaks currently seen in the forecast maps. Of course, the longer out the forecast, the more things can change, so I will continue to watch for any signs of very cold conditions, but so far I don’t see anything on the horizon. Rainfall is expected to be near to below average for the next few weeks.

The big wildcard in all of this is the tropics. You may recall that there was almost no activity in the Atlantic in July and August. This was due to the combined effects of colder than average ocean temperatures and prodigious amounts of dust coming off the Sahara, both of which prevented the development of strong systems coming off of Africa. This all changed in the last two weeks. Tropical Storm Gordon developed in the Caribbean, where ocean temperatures are much warmer than average, and followed the atmospheric circulation around the west side of the high pressure up into Mississippi and Alabama as well as inland areas to their northwest. It’s still there as a remnant patch of moisture, but the same high will keep that moisture well off to our north and west, eventually heading east through the Ohio River valley, but it is not expected to have much impact on us here in the Southeast.

What was good for Gordon is bad (for us) for Tropical Storm Florence (recently downgraded from a strong hurricane). The same high pressure area is steering Florence almost due west. We originally though it would curve to the northeast and stay out to sea, but the strong high pressure has continually pushed it farther to the west of its expected path. The latest computer models indicate that it could be close to the East Coast of the US by next Thursday. Right now the models are all over the place about whether it will make landfall or curve north and barely miss us. The most likely places for Florence to hit (if it does make landfall) are the Carolinas or farther north in Virginia or New Jersey, but there are a few model paths which indicate that it could be coming in farther south in Georgia or even Florida, so it’s important to keep an eye on the forecasts. It’s got a lot of warm water to traverse too, so it is likely to become a hurricane again before it gets close. If it does go up the East Coast through the Carolinas and Virginia, we could even benefit from sinking air outside the main storm, which could make things even drier and warmer than expected. Forecasts could change pretty quickly as the path of the storm becomes better known, so make sure you are looking at forecasts more than once a day by mid-week. Note that your regular garden-variety weather apps for your smartphone do a lousy job of giving you good forecasts in rapidly changing conditions, so don’t depend on them to tell you what is actually going to happen a few hours ahead of the storm’s approach.

Farther down the pike, there are two more developing systems in the eastern Atlantic that are likely become named storms in the next two days. Investigation 93 (just now labeled as Potential Tropical Cyclone 8) is expected to become Helene and is currently expected to curve to the north and stay out to sea. Investigation 92 has a 90% chance of becoming a tropical cyclone and would then become Isaac. Don’t get fixated on the names, because if 92 develops first it would be called Helene and the Potential TC 8 would then become Isaac. Either of them would take ten days or more to be a factor in our weather, so nothing to worry about at this point. There are also two more waves over Africa that are headed west towards the Atlantic which could develop later in September, but that is a long time from now. Remember, we still have half the tropical season to go, so more storms are likely before this year is over.