This was posted on FB by Steven Nelson, forecaster at NWS Ptree City office. Pretty sobering stuff:
For PTC and north Georgia friends, here's the latest update on Helene.
tldr; Helene will produce Opal-like (1995) rainfall and flooding and Hugo-like (1989) inland wind impacts. Google those storms and prepare accordingly. Sleep downstairs/away from windows Thursday night. Prepare for extended power outages.
The heavy rain that was forecast began today and will continue in waves tonight, tomorrow, tomorrow night, Friday morning
. By that point we should have around 6 inches of rain with a 10% chance of seeing ~9 inches. See the map below for even more ridonkulous worst-case/90th percentile amounts in the NE GA/W NC mountains. and box and whisker rainfall plot for Peachtree City. Yea, we need the rain but not so much over so fast please.
River forecasts from US National Weather Service Southeast River Forecast Center are taking many points from drought levels to major flood stage (10-50 year flood event) in just 12-24 hours.
The inland wind impacts Thursday night and Friday morning will be unprecedented. In response to a deep upper low to the west, Helene is using that "Fujiwara-slingshot" itself north at 30 mph (Michael's NE motion was only 15 mph at landfall), maintaining hurricane strength perhaps as far north as I-20. This swath of high winds will extend well east all the way to Augusta and into SC. See the wind gust box and whisker plots for Tallahassee, Albany and Peachtree City below. It will be bad here but Tallahassee is really in the crosshairs.
I can't find data on Hugo's forward speed but it's intensity was 140 mph at landfall. It carried hurricane force winds so far inland it destroyed 1/3rd of the harvestable timber in South Carolina (over $1B in 1989 dollars), enough to build 600,000 homes. Michael also produce $1B of forestry loss and $2.5B of agricultural losses and 400K without power. Irma peaked at 1M without power. Helene will likely exceed the wind impacts of Frances, Opal, Irma and Michael and may even surpass Hugo in the amount of inland treefall, agricultural loss, damaged homes and number of customers without power.
There's still time to stock up on water and other necessities tomorrow before the strong winds arrive. Once winds exceed 35 mph, power companies will not respond, at ~50 mph first responders won't either. Prepare for being without power for an extended period. Irma (2017) knocked out power in DeKalb county for 3 days. Forecasts and storm response by first responders, state and local government, Georgia Forestry Commission, power companies and others are much better these days. Most areas won't see outages that long, but some will.
The east winds will hit hard Thursday night. If you have large trees and tree limbs near and especially to the east of rooms where you and your family sleep, I strongly recommend sleeping downstairs and away from any windows. Keep your cell phones charged and near your bed to alert you to any tornadoes or level 2 or 3 flash flood warnings. The flashlight also comes in handy.
If you read this far, please help spread the word to family and friends in the path of this storm, especially those in their later years or that may not use social media or watch the news. A phone call might give you a chance to catch up and let them know you're thinking about them. Stay safe everyone!
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