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Irene, High Tide, and a New Moon...
Posted by Erica Grow, Meteorologist on August 30th, 2011 at 04:05:00 pm
It was a recipe for one of the highest storm surges in Connecticut's history. You probably heard me and my colleagues here at News 8 talking about the astronomical high tide caused by a new moon, coinciding with the arrival of Hurricane Irene from the southwest. The water level at high tide is already elevated during full moon and new moon cycles, and the strong winds wrapping around Irene were perfectly positioned to funnel Atlantic Ocean water in between our shoreline and Long Island. The water had nowhere to go but inland.
I believe this will end up being one of the costliest natural disasters in Connecticut's history, and most of the damage is due to this storm tide- the combination of storm surge and high tide cycle.
A couple of our viewers asked, "what is astronomical high tide, anyway? And why does that make a difference?" You may already know that the tide is dependent on the movement of the moon. The moon's gravitational pull actually causes the bodies of water on Earth to rise up toward it. If you were to look at this from outer space, you would see a relative high spot- a "bubble", if you will- of water, carefully following the path of the moon as it orbits Earth. When we experience high tide, that bubble is moving through our area.
We experience high tide twice per day, no matter what. However, the tide varies with the lunar cycle, and that's where astronomical high tide comes into play. Let's take the new moon, for example, which occurred on Saturday night as the hurricane was approaching. The moon is not visible because it is fully in shadow, not reflecting any of the Sun's light. That means the sun is directly behind Earth (from the moon's perspective, of course). The perfect alignment of the Sun with the moon enhances the gravitational pull on Earth's water bodies- enhancing the "bubble", you might say. The same thing happens during a full moon, because the properties of solar-lunar alignment are the same.
So basically, the timing of Irene's arrival is one of the factors that made it so devastating. The storm surge still would've been significant, but if the storm hadn't made its approach during high tide, we could've avoided some of Irene's worst effects.
4 comments
Erica…just a few corrections to your analysis of Irene: First, several hurricanes have caused higher storm surges in Connecticut (and Long Island) than tropical storm Irene: Hurricane Carol (1954) had higher storm surges in eastern Connecticut (up to 10 feet above msl), while the 1938 Hurricane had much higher storm surges east of New Haven (perhaps as high as 12 above msl).
Next, although certainly the astronomical high tide caused by a new moon, coinciding with the arrival of Hurricane Irene making landfall at the same time had a significant effect on tidal flooding in Connecticut….the real culprit was the TRACK of hurricane Irene. Most (in fact just about all) tropical cyclones approach the Tri-State area (Long Island/Connecticut) in a “northeasterly” direction of movement. This type of path keeps the much stronger eastern semi-circular of the cyclone well east of Connecticut/Long Island …with the worst winds and most of the storm surge power spent over the open sea (or out of the far eastern Rhode Island/Cape). This is why, despite many hurricanes move parallel the East Coast (like Bob (1991), Donna (1960), Carol (1954), Edna (1954), the 44 Hurricane….ect few pf these storms ever produce “sustained” hurricane force winds along the Middle Atlantic coast. Only the 1938 hurricane, Hurricane Belle (1976 – a weak storm with 70-75 mph winds), and Hurricane Gloria (1985) tracked in a way that the “bulk of the severe eastern semi-circle passed over the bulk of Connecticut”. Irene had a landfall right near NYC – thus the “entire state of Connecticut was dead center in the worst eastern half of the cyclone”. I drove from Groton Long Point to Westport, and the number of trees down and even areas of overwash were the same.
Finally, tropical storm Irene was the worst storm to strike Connecticut since Hurricane Gloria in 1985, no doubt about it – however Hurricane Irene is NOWHERE NEAR AS DAMAGING TO CT/LI/RI AS THE 1938 HURRICANE! True, Irene will be a billion dollar storm, but this is due to inflation (2011 adjusted dollars), and the cost of repair and cleanup costs. The 1938 HURRICANE DESTROYED 170,000 STRUCTURES in Connecticut, Long Island, and Rhode Island – Irene destroyed a few hundred (maybe). 700 people were killed in the 38 cyclone, islands were cut in two, and whole coastal communities on Long Island and Rhode Island were swept out to sea (people, stores, roads, schools…etc). Irene was a summer thundershower compared to the 38 cyclone. Officially, Irene was a tropical storm at landfall (65-mph winds – 965 mb pressure)….the 1938 Hurricane had 115-mph winds and a 946 mb pressure at landfall). Survivors of South County Rhode Island claim they saw a 30 foot tidal wave strike the coast near Westerly, Rhode Island.
This is the bar for hurricanes in this region:
http://www.oocities.org/hurricanene/hurr1938.htm
ah-haaa... i see said the blind man as he picked up his hammer and saw... two astronomical bodies pulling together at the same body of water... duuuh, jeff... thank you professsor erica...!!! 
To SI... if you are not a meteorologist, I think you might've missed your calling! I think you might've misunderstood the preface of my blog post. I said that Irene was a recipe for one of the worst storm surges in state history; I did not claim that it was the worst storm surge we've ever experienced. And I decided to focus on the unusual coincidence of high astronomical tide with the approach of the storm as one of the main causes of this high surge. Of course, the storm's track, just barely grazing the western portions of the Sound, played the biggest role in the surge... it would be negligent of me to ignore this! ...did the change in weather or astrological bodies last week have anything to do with the Boston Red Sox 'melt-down'...??? 
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