Flooding In The Palmetto State

20151004_WV

In a scene that Texas deals with, heavy rain and flooding. This time it is in South Carolina. They have been getting heavy rain this past weekend. Here is a rainfall map for the past seven days.

20151005_7Day_Rainfall_Total

Many areas have seen between 10 to 20 inches of rain. Some areas have seen nearly 30 inches of rain! That is a lot of rain. I would not be surprised if some areas get 3 feet of rain once it is all over. It is no wonder, they have severe flooding in South Carolina. It has so far claimed 11 lives.

So, how did this all happen? Many factors come to play. The moisture is an atmospheric river from Gulf of Mexico and Hurricane Joaquin, which was forecasted to make landfall on the Eastern Seaboard. It went out to the Atlantic after lingering over the Bahamas hammering the island nation with strong winds and heavy rain. There is also a trough over the Southeast US, which shunted Hurricane Joaquin out to the Atlantic. The negative tilt of the trough made the storms stronger. There is also upper leveling ridging over Canada. The combination of the two allowed easterly wind flow into South Carolina, giving them higher than normal tides. That causes flood waters to be blocked and beach erosion.

20151005_500mb_GeopotentialHeightAnomaly_NA

There is also a large area of 2 inches of precipitable water (PW) over Bahamas and Atlantic at the 850 millibar or 5,000 feet level. PW measure depth of liquid water at the surface that would result after precipitating falling as explained by Nation Weather Service. The huge PW is largely from Hurricane Joaquin.

20151005_850mb_PrecipitableWater_NA

It is like an atmospheric river, like the Pineapple Express that sometimes hits the West Coast of America. The training and relentless heavy rain over the same area reminds me of the October 1994 Flood that hit Texas on October 15-19, 1994. Many areas saw widespread totals of 10 to 20 inches including some areas seeing over 30 inches of rain.

October1994Flood_850mb_PrecipitableWater_NA

The setup is fairly similar, moisture from what was East Pacific Hurricane Rosa, slow moving upper level trough over Western US and upper level ridging over Canada. The ridging made the upper level trough linger, which caused a Pacific front to move slowly on top of a warm front over Southeast Texas. The October 1994 Flood happened in an El Nino like the South Carolina floods.

October1994_500mb_GeopotentialHeightAnomaly_NA

Once the heavy rains are over, it is going to be one of South Carolina’s worst flooding. Terrible time for that state. Let’s hope it does not get any more worse.

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