Some Straight Talk About the Flood Potential in the Middle Atlantic States

By -
As more data has come in today, the potential for catastrophic flooding (similar to Hurricane Agnes' flooding or worse) exists for the Middle Atlantic Region. 

 The bottom line: it is likely some areas will flood that have never flooded before. Prepare NOW to evacuate you and your family. If you are given an evacuation order, please comply immediately before roads get clogged and chaos commences. Please read on.

Meteorologists hate being wrong and I would love to have the luxury of waiting for more data to write this (meteorologists always like "more data"). But, given the magnitude of the disaster potentially ahead of us, and given the increasingly limited time to prepare, I am writing this now. Please take this seriously. I have been doing this for five decades and I wouldn't write this and put my reputation at stake if I weren't seriously concerned about what may occur. I am also trying to put myself in the position of a family living in the threatened area.

If I had to pick a single weather forecasting model, it would be the ECMWF. It, and the other models, are forecasting giant amounts of rain. Here is the latest ECMWF:
click to enlarge
The maximum amount forecast (in between individual weather stations) is more than 30 inches!! Yes, it is entirely possible the rain pattern could shift a bit north/south/east/west and it might "only" be 20 inches. Regardless, it appears a major flood event is on the way in the Middle Atlantic region.

What makes this even worse is that during the last 30 days more rain than usual has fallen over most of the area where Florence's heaviest rains are forecast to fall. The map below is the number of inches of rain above (green/blue) or below (reds/yellows) normal over the last 30 days.

In much of western Virginia, Maryland and eastern West Virginia, it has been wetter than normal.
With already wetter than normal conditions, the excessive rainfall from Hurricane Florence will...
  • Run off more quickly than usual into...
  • Rivers that are already higher than usual.
All of this may equal tremendous or even catastrophic flooding.

For perspective, I went back and looked at the ECMWF four days before Hurricane Harvey's torrential rain began in Houston. The maximum amount forecast for the region was 29 inches. The heaviest actual amount was 60.58 inches! The model's peak rainfall forecast was less than half of what actually fell. With Harvey more than 13,000 people had to be rescued in metro Houston.
Hurricane Harvey flooding in southeast Texas, 2017
If thirty or more inches of rain fall with Florence, more than 13,000 may need to be rescued over a much larger and more remote area (as opposed to concentrated in a major city) which means far more resources will be required. If I were an emergency manager, I would be looking to bring people in from outside of the region NOW, especially expert applied hydrologists.

By comparison, 1973's Hurricane Agnes caused record flooding in the Middle Atlantic region with less than 15 inches of rain over Virginia and West Virginia. So, it can happen even if much less than the ECMWF's 30 inches fall.
Richmond flooding from Hurricane Agnes, 1973
So, What Do I Do Now™?
  • My suggestion that emergency managers bring in extra help in advance is above. 
  • My preparation suggestions for individuals and families are here. 
  • Health suggestions pertaining to waterborne illness (from Ascel Bio) are here. 
I will likely update all of this tonight if there is enough extra data to justify it. After all of this research and writing, I'm going to watch my Chiefs for a while. 

Comments

Post a Comment

Popular posts from this blog

Hilary's Forecast Path Shifts West; Updated 9:20am PDT

By -
Image
The forecast path of the center of Hilary has shifted a bit to the west. This increases the threat to the Southland, especially in terms of flooding.  Rainfall Note the heavy rains are forecast for Los Angeles County. Serious flash flooding may result. Because the forecast path has shifted to the west, that increases the threat of serious flooding in Los Angeles County north into Yosemite and the southern Sierra. It lessens the threat in Utah and western Arizona. While the threat of widespread flooding in Utah and Arizona lessens, note that some thunderstorms with localized heavy rain show up on the map.  In Nevada, the more western path increases the risk of serious flooding around Mt Charleston and into the central part of the state.  Here is the updated  (9am PDT) flash flood risk map. Wind There are already about 40,000 people without power in California, mostly in the center of the state.  The maps above are the peak gusts forecasted with the storm. The highest winds, in general,
Read more

Dangerous Travel Conditions - People Reportedly Stranded

By -
Image
-- Note, more current info available. Scroll up. --- Updated Information as of 8am PDT You are risking your life if you attempt to travel through the purple area.  While the rain has not begun in coastal California, I would urge you to use this time to make any preparations. Power outages have occurred already in southeast California. Here is the latest radar as of 7:55am PDT. As of 6:40am PDT , the radar indicates moderate to heavy rain falling over desert areas of Southern California and far western Arizona (click to enlarge).  Rainfall amounts for the 24 hours ending at 7am PDT show more than two inches have already fallen. There are reports from reliable sources that roads are already washed out and that people are stranded in isolated parts of the desert.  Below is a high-resolution computer model's rainfall forecast from 5am PDT to 11pm PDT Sunday. More than a foot of additional rain is forecast to fall. This will lead to catastrophic flooding.  Here is a map of current watc
Read more

Update on Tornado and Wind Potential; 12 Noon PDT

By -
Image
There was at least one tornado and at least one funnel cloud yesterday.  --- original forecast --- Hilary (the swirly symbol) continues to move NNW paralleling the coast of Baja California, Mexico. The area outlined in red has a significant risk of tornadoe s the rest of the afternoon.  Below is a list of peak wind gusts so far.  Peak winds may increase farther north as the afternoon progresses.  Addition at 12 noon PDT: Sure enough, winds have increased.  Note: If you are in the San Diego area, I recommend not  traveling east on I-8. Heavy rains may cause flash flooding that will involve the highway. 
Read more