Wednesday, May 28, 2014

High tides and no wind - what is going on?

As I write this the tides in our area are running almost a foot above predicted from astronomical calculations.
Why is that?

The NOAA Extra Tropical Water Level guidance is located at

In this blog I want to note the anomaly that often occurs along our coast.

By anomaly I mean a higher water level that is not explained by normal astronomical tide prediction or the wind. Or, as stated in the manual associated with the guidance

From the NOAA Manual that is linked to the site "This "Anomaly" is averaged over 5 days, and is then added to the future predictions of the tide and storm surge to predict the Total Water Level"

Now here is an example - .

The lines are defined at the top of the plot. 
The black line is the 'Total Water Guidance' that includes both the storm surge and the anomaly. 

In this case the surge contributes about .3 feet for a day or so then goes to zero

The Anomaly (Green line) is about 0.5 feet. 

The question is "What is the anomaly?" This is important because with the added Anomaly the water levels will be over the highest 18 year tides and will flood some streets in coastal cities. 

Dr. Tal Ezer at Old Dominion University has found that the anomaly is related to the speed of the Gulf Stream. He has found that the transport of the Gulf Stream is well correlated with our water levels: the Gulf Stream slows down and our water level goes up or the Gulf Stream speeds up and our water level goes down.

Dr. Tom Rossby (URI) has a paper out with an analysis showing no slowing of the Gulf Stream.

This is an area of active research.