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What to expect from Dorian

/ September 4, 2019 at 9:08 AM

Dorian Day 1 has arrived in the Lowcountry. Clouds from the storm’s outflow have been blanketing the area for about 12-15 hours now, and the first rain bands are approaching shore. Here’s what to expect over the next couple days.

Wednesday

Weather will gradually head downhill today as Dorian approaches the area. Off-and-on heavy rainfall thanks to rain bands will start this morning. Winds will be increasingly breezy with stronger gusts within bands. By later tonight, expect winds to continue to increase, with sustained tropical storm force likely east of 17-A by Thursday morning.

Tidal flooding will be the first significant impact from Dorian. A 9.3′ high tide is forecasted around 1:03 PM. I would expect salt water flooding to begin sometime well ahead of the time of high tide, perhaps as early as 11 AM. A 9.3′ tide will cause substantial flooding problems in downtown Charleston, rain or not. Add rain and more widespread flooding will become likely. Rain bands will need to be watched very closely for coinciding with high tide.

As the day goes on, expect rain and wind to increase. We should see a significant deterioration in weather after sunset, with the risk for flash flooding increasing as the night wears on. A Flash Flood Watch goes into effect at 5 PM. As rainfall increases with the approach of an extremely high tide a little after 1am Thursday, there is potential for significant flash flooding in downtown Charleston. Numerous roads may become impassable and structures may flood, especially on the east side of the peninsula. Downtown will be very dangerous for travel, I suspect.

Tornadoes will also be possible on the north side of Dorian’s circulation. The risk for tornadoes will be greatest from the coast to 17-A. These tornadoes may not be very strong and won’t last long, but they can still cause problems in a very quick amount of time. Be on guard to receive warnings and head to your safe place if you’re riding this out at home.

Action item: Make sure you have redundant, reliable ways to receive weather alerts and that they can wake you. Flash Flood and Tornado Warnings will ring through to your cell phone via Wireless Emergency Alerts. If you normally silence your phone at night, consider leaving it off silent so the emergency tones can alert you.

Thursday

No sugarcoating it: Thursday is going to be a pretty rough day as Dorian makes its closest pass to Charleston (somewhere around 40-60 miles offshore). Sustained tropical storm-force winds will be common, especially near the coast. Hurricane-force gusts — and perhaps even a period of sustained hurricane-force winds — are not out of the question the closer to the water you go. Numerous power outages and downed trees appear likely.

The highest risk of flash flooding will be very early Thursday with the 1:11am high tide. This tide could top 10′ in the harbor for only the third time on record and the first time since Hugo. Let’s hope that doesn’t happen, but if it does, a long-duration salt water inundation event will be possible downtown.

Additionally, flooding due to heavy rainfall will likely develop all over the Tri-County area. Vulnerable areas like Shadowmoss, parts of Summerville, College Park near Goose Creek, and along the Ashley and Cooper rivers should be prepared for surge and heavy rainfall combining to produce high water levels. Flooding is not going to be concentrated to downtown! If you have had flooding problems in the past, it is likely you will see issues with Dorian.

A Storm Surge Warning will remain in effect throughout the event. Note that the warning takes in areas up the Ashley and Cooper, up toward Hanahan and the old Navy Base, as well as reaching well into West Ashley close to Summerville.

As the center of the storm moves up the coast, winds will shift sharply to the northwest. Once this happens, the storm surge will be blown back out into the ocean. Heavy rainfall and strong winds will continue to be a threat into Thursday afternoon before Dorian pulls away Thursday night. Expect weather to improve as we get to sunset Thursday, with sunny skies developing Friday.


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