Tuesday, January 17, 2017

Rain, Winds and Tides

The NWS just updated their discussion with information from the 3:00 model run.  There is some interesting stuff in it.....  Especially good news for Pluviophiles... (Rain Lovers)  We are settling into about 24 hours of an "Atmospheric River" that is being fed with moisture from just north of Hawaii...  Rainfall amounts will be impressive.  This afternoon was the appetizer....  Hourly rainfall rates have been running about .25 to .5 inches per hour off the coast.  One to two inches of rain between now and tomorrow afternoon here is not out of the question...  But wait...  There's more....  The wind has been screaming all around us.  There has not been a Port Townsend ferry run today.  All runs have been cancelled due to high winds...  Yet we have not been affected.  This is due to the Olympic Wind Shadow...  It is coming from just the right direction so we can hide behind the Olympics.  This could change at any time though...  A little tweak in direction and we will have some wind.... As if this isn't interesting enough, the barometer is dropping like a rock and tomorrow morning at 9:13 we will have an 11.14' high tide.  A low barometer and high "king" tides are a bad combination.  Right now the barometer is at 29.51" or 1000mb and falling rapidly.  At this rate, the actual tide will be at or above the 12 foot level.  The NWS has issued a coastal flood advisory for the San Juans and Bellingham area.  Something worth watching...  On my site I have a tidal adjustment number that shows the impact of barometric pressure on the tides.  Right now the tides are 5" higher than predicted.





This graph shows how fast the barometer is dropping....


Typically, the wind begins when the barometer starts going up.... It could be a long 24 hours...

1 comment:

  1. In this blog I did not go into detail about the relationship between barometric pressure and tide levels. I’ll share some details here. Barometric pressure is just that… Pressure. The higher the number the more pressure we have in the atmosphere at sea level. As the pressure increases, it “pushes” the water level down. When the pressure decreases, the water levels rise. The “forecasted” tide levels use an average barometric pressure of 29.91” or 1013mb. If the barometric pressure is lower than these values, sea level will rise above the forecasted level. Tide charts are all forecasts with an assumed barometric pressure.

    A few years ago I was at a party and heard a comment about king tides. This person stated that low barometric pressure can raise the tide by 3 feet….. I knew that couldn’t be true, but I didn’t have the science or math behind it. So… I did a little homework and put together the algorithm to calculate the barometric pressure impact on tides. I put that formula into my website. It calculates the real time impact as well as a chart for reference.

    I used the term “king tide”. King tide is kind of a slang term for the winter high tides. The highest tides of the year are in the winter time. I was fire chief in this area when we had the perfect (well… not so perfect) trifecta. King tide, low barometer and 50mph winds from the southeast (very rare direction)…. Very few bulkheads could handle this combination and there was a LOT of property damage. I saw a 12” concrete bulkhead broken into pieces. I saw submerged cars, ruined shops and severe home damage. It was right up there with one of the worst experiences of my life seeing all the damage, pain and suffering of the folks who were impacted by this.

    Complacency can be our worst enemy…. Yes… we can have that rare, very localized catastrophic storm here.

    Edit... As I typed this, the wind is picking up... gusting to 36 so far....

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