13 September 2018

Florence's wind and rain reaching eastern North Carolina; also watching Helene, Isaac, Joyce

It's been two weeks since Florence formed, and early Thursday morning, the first rainbands and tropical storm force winds from this long-track hurricane have reached Cape Hatteras and Cape Lookout (lots of radar loops).  At 8am, the storm was centered 170 miles east-southeast of Wilmington NC and moving toward the northwest at 12 mph.  Maximum winds in the eyewall fell to 110 mph, making it an upper-end Category 2 hurricane.  It is not expected to strengthen anymore, even as it passes over the warm Gulf Stream today.

However, THERE'S MORE TO THE STORY THAN THE CATEGORY. While the peak winds have fallen, they are still strong enough to be destructive to houses and trees, and the water-related threats (storm surge and rain) remain a very big concern.  Tropical storm force winds extend up to 200 miles from the center.

The storm has grown in size over time as they typically do, so although the peak winds are weaker than they were, the storm surge threat has actually increased for more of the coastline. The storm surge warning from Cape Fear to Cape Lookout still includes a potential for 9-13 feet of storm surge, on top of the normal tides (flooding will be worse around high tide, and a slow-moving storm will stick around for at least one tide cycle). Now that the landfall trajectory is fairly locked in, here are some storm surge inundation maps for the Cape Lookout and Cape Fear areas, but I encourage you to peruse it in more detail at https://www.nhc.noaa.gov/refresh/graphics_at1+shtml/093018.shtml?inundation#contents
You can also monitor relevant tide gauges at https://tidesandcurrents.noaa.gov/quicklook/view.html?name=Florence

Rainfall has been and continues to be a significant danger.  A tropical cyclone of any intensity can dump feet of rain if it moves slowly, and Florence is no different. 20-40 inches of rain could fall over parts of eastern North Carolina which would easily induce tremendous flash flooding. Even further west into the mountains, 6-10 inches of rain could fall. The rain will persist for a few days in this region.  The latest forecast does not indicate quite as much of a prolonged stall, but rather a gradual drift westward then turning northward out of the Carolinas by Monday.

Only 29 hurricanes have made landfall within 100 miles of Wilmington since 1851... the most recent was Arthur in 2014, and the most intense was Hazel in 1954.  Florence will become the 30th tonight.

A brief overview of the rest of the tropics, which are bursting with activity.  Hurricane Helene is quickly disintegrating as it heads north over cool water, Tropical Storm Isaac remains disorganized as it passes over the Leeward islands, Subtropical Storm Joyce is spinning innocently well west of the Azores, and that pesky disturbance in the Gulf of Mexico is still a rainfall threat for Texas this weekend.

Since Joyce formed yesterday, the season is up to 10 named storms, 5 hurricanes, and 1 major hurricane.  In an average season by this date, we'd have 7 named storms, 3 hurricanes, and 1 major hurricane. In terms of ACE (Accumulated Cyclone Energy), the season is at 127% of average for the date.

No comments:

Post a Comment