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Thursday, September 1, 2011

Was Irene Hyped?

I'm stealing one of Geoff's blog entries now.  One of his good friends, Bob Hart, a renowned expert in tropical meteorology and a North Branford native wrote an essay recapping the coverage of Irene on FOX CT. I obviously like the fact that he complements our forecasting.  But even better...he recaps the storm, discusses the hype factor, and addresses Irene's forecasting challenges.

"First, I wholeheartedly agree with the replies here noting the quality of the forecasts by Geoff and Rachel. If this storm were to happen again, I would not ask that the forecasts be changed in any significant way for CT.

While several of those who received little impact from Irene (or those watching from afar, or the masochistic wanting damage) are claiming hype, those who truly were impacted in a serious way are generally not.

I was on the CT coast for Irene and visited a few towns, including that where I grew up (I still have family there). I’m willing to bet a large sum of money that if you asked those impacted by surge (Milford, Branford, Guilford, and beyond) – whether the storm was worse than Gloria – they would say yes.

In fact, my reading of the surge numbers in Bridgeport, New Haven, and elsewhere on CT at least are that they were comparable to category 2 hurricane estimates!

Was this due to the high tide and new moon? In part, yes – but only in part.

Can we forecast the timing of landfall to within 6 hours two days out to make that determination? Absolutely not.

In fact, Irene arrived many hours earlier than the two day forecast (when watches are issued). This is why it is important to consider the range of possibilities in a forecast, as there is an (unspoken) “cone” of uncertainty about intensity just as there is a well-communicated cone about track.

Yet, I suspect if you asked those at the Massachusetts border they would say they barely got tropical storm conditions, and they might be right (I haven’t seen much data since I was out of internet access until my Delta flight right now, ironically!).

Let’s pretend for a minute that we knew from the start that Irene would be a tropical storm when it crossed CT – let’s pretend that only tropical storm warnings were issued from central NJ northward. My bet, with a lot of money, is that the loss of life would have been greater, perhaps much.

A weakening major hurricane crossing as a tropical storm produces much different impacts than a tropical storm that is stable. These generally include storm size, the accumulation of wave growth and surge, as well as model performance. And yet the warnings cannot discriminate between these.
We are a spoiled society. I don’t think that most in NYC realize how much worse it could have been, how close they came. They should look at how far the surge went in CT and LI. Seawalls completely destroyed and pushed inland dozens to hundreds of feet. I saw it in CT.

No doubt those in low lying areas of NYC remember December 1992 when the subways flooded and the FDR and other major routes were covered in water. Many areas on coastal CT approached or exceeded that storm. I suspect those who lost their homes completely in CT and LI (out to sea, yes, there were several in CT and elsewhere where literally only a foundation was left) would gladly have traded their epic loss for a weekend of board games and wine with the family as the only “inconvenience”.

This is the problem with the categorization of hurricanes. The number is primarily associated with wind. Yet, the surge is not entirely (in fact, far less) explained by the wind. The rainfall is almost completely unrelated to the strength of the wind.

The surge in CT was equivalent to a typical category 2 (between Gloria’s surge and 1938’s record surge) while the wind was strong tropical storm (although the post-season analysis will determine that concretely). A moderate to even upper category 1 forecast landfall was exactly the right forecast two days before landfall, when watches were issued and evacuations considered, given the guidance.

And then there is a specific nature of the wind definition of category. The definition of the Saffir-Simpson category is the estimated strongest SUSTAINED wind (1-minute average) at 10-meter elevation anywhere in the storm at that time, assuming open exposure over land. Yes, anywhere in the storm. This means that 99.44% (thank you Ivory soap) is less than that maximum. And most places are much less given the structure of hurricanes.

In fact, almost by definition, the strongest wind in a hurricane is NEVER observed by people or their homes. So a true marginal category 1 hurricane in CT is quite likely to only produce tropical storm force sustained winds across the coastal population and in many well inland areas not even that.

And yet, while being a likely tropical storm in CT at the end, Irene produced a remarkable extent of 50-75mph gusts across a broader region than almost any prior tropical storm on record (well into RI) due to its unusual structure (topic for another day).

And that above tricky definition is the rub.

A colleague at NHC (Dr. Mike Brennan) forwarded some observations from Katrina (category 3 landfall). Do you realize that not a SINGLE official land-based station reported sustained hurricane force winds? Repeat, no official category 1 sustained winds in Katrina on land.

Sure, plenty of gusts – plenty – to hurricane force and even a few to category 2 or 3, but no sustained hurricane force winds.

Even at official marine sites, there was no reported sustained wind above category 1 (six sites reported hurricane force sustained winds, but none above 76kt). If a storm like Katrina which 1) was also huge, 2) so much more intense and 3) hitting an urban area, cannot produce a hurricane force sustained wind on land, we cannot expect the same in CT even if Irene was a category 1 hurricane– unless there is amazing chance.

That chance happened in Bridgeport with Gloria. Gloria produced a 64knot sustained wind in Bridgeport. It was the only sustained wind observed at an official station in CT. And it was by chance, given the track.

In the end, I think our definitions are flawed. We should not be defining a storm by the peak sustained wind intensity which is almost never truly observed. It is for this reason that perhaps millions in south Florida think they experienced category 5 winds, when perhaps a few hundred did (if that).

Finally, I have never seen a track forecast for a New England tropical cyclone as good as this one. NHC, the models they use as guidance, and the scientists who work extremely hard on their developments are to be commended. The actual track the storm took has only occurred a handful of times (perhaps a few fingerful, I won’t pick which fingers) since the 19th century. And while there was some uncertainty of track (over Philadelphia, over NYC, over Boston), it almost never was forecast to go out to sea 4-5 days out (and longer). This is astonishing.

Remember Floyd in 1999? The track was all over the place 4-5 days out. Hugo in 1989 was forecast to come up the coast originally!

Irene was a landmark event for track forecasting for New England, but we should not be spoiled by this. Don’t count on this confidence next time.
As Geoff mentioned, he slightly lowered the rain and wind forecasts Saturday night. It was the right move, and it was the correct forecast. It was the scientifically correct decision without jeopardizing preparation, since people had already prepared. It was a tough decision and not everyone made the same decision, but it was correct from a scientific perspective yet very difficult from a communication perspective.

As part of my classes, I require my students to forecast (and I forecast along with them as any meteorologist worth their salt will do, no matter what the alphabet soup at the end of their name says). I cannot do what Geoff and Rachel do, and I assure you that very few in the world can. Very few jobs in the world require you to be an expert on snowstorms, icestorms, floods, hurricanes, computers, and top-tier communication and improvisation. Oh, and a very thick skin at times. Although I imagine it is very rewarding in the net, I suspect you don’t want their job.

In light of all the above, the consequences at play, and having gone through Irene and having watched Geoff’s blog, and Geoff’s and Rachel’s forecasts for days, I applaud them. People and property were saved during this storm by their forecasts, and their very effective communication of those forecasts.
CT is very lucky to have Geoff back on the air. Now if only our schedules would cross paths so we can meet up for poker.

Bob Hart
Florida State University"



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