Update on the possibility of another “perfect storm.”

Briefly, tonight it appears that chances are somewhat higher for another “perfect storm” this weekend/early next week (see last post), but still quite small. Just be aware, if you live on the US or Canadian eastern coasts.

NHC cones Oct 24 8 pm

Tonight’s NHC 5-day forecast track showing cone of uncertainty and forecast track of center of storm. (Wunderground)

The NHC’s take

The National Hurricane Center’s forecasters have moved their forecast a bit closer to the eastern seaboard, but still only the very left of their forecast cone grazing the coast and at the places you might expect (like Cape Hatteras, Mid-Atlantic coasts in a couple of places, eastern Long Island, southern Connecticut, Rhode Island and Cape Cod). They keep the forecast track of the storm’s center well out to sea.

Before mentioning the NHC discussion, I just want to point out that you do not have to be a scientist, try to understand all the details they talk about, or know what computer models they’re talking about (though an overview is nice to have, it’s not necessary). The 5-day forecast graphic is all you really need to know.

OK, here’s the NHC explaining the change at 5 p.m. Eastern today (note: I added emphasis and left the text in caps so you’ll know that I copied and pasted it from the NHC site – apparently everybody yells there):

ON DAY 2…A TURN TOWARD THE NORTH-NORTHWEST AND A SLOWER FORWARD
SPEED ARE SHOWN AS SANDY INTERACTS WITH THE ABOVE-MENTIONED
UPPER-LEVEL TROUGH. AFTER THAT TIME…SANDY IS EXPECTED TO TURN
NORTHEASTWARD AS IT BEGINS TO INTERACT WITH A LARGER UPPER-TROUGH
MOVING INTO THE EASTERN UNITED STATES. WHILE THERE IS STILL QUITE A
BIT OF EAST/WEST SPREAD IN THE GUIDANCE AT DAYS 4 AND 5…THE GFS
HAS TRENDED TOWARD THE SCENARIO THAT HAS BEEN SHOWN BY THE ECMWF OF
MORE INTERACTION WITH THE TROUGH. WHILE THE GFS TRACK HAS SHIFTED
WESTWARD AS A RESULT…THE ECMWF HAS ALSO SHIFTED WESTWARD THIS
CYCLE. THE NHC FORECAST HAS BEEN ADJUSTED TO THE LEFT AS WELL…AND
LIES ABOUT HALFWAY BETWEEN THE ECMWF AND THE GEFS ENSEMBLE MEAN AND
THE FSU SUPER ENSEMBLE AT DAYS 3 THROUGH 5. THE UNCERTAINTY IN THE
LONG-RANGE TRACK FORECAST REMAINS VERY HIGH…AND IT IS TOO EARLY
TO DETERMINE SPECIFIC IMPACTS FOR THE U.S. EAST COAST NORTH OF
FLORIDA.

They say “north of Florida” because various tropical storm warnings or watches have already been issued along much of that state’s Atlantic Coast below roughly Jacksonville.

Jeff Masters’ take

Dr. Masters posted last at about the same time as the NHC discussion above.

While going into the flooding threat in more detail, if this does hit the Northeast, he also says (I translated the technical term):

There remains a lot of model uncertainty on where Sandy might go, and I still give a 30% chance that the storm will have a minimal impact on the U.S. An extra set of balloon-borne radiosondes [weather balloons] is going to be launched at 2 pm EDT on Thursday all across the U.S., which should help tomorrow evening’s model runs make better forecasts of where Sandy might go. Extra radiosondes [weather balloons] will be launched every 6 hours through Saturday afternoon.

FFC_27Apr_18Z

Something you get from radiosondes, probably. This skew-T chart, from April 27, 2011, forecasts tornadoes. (Source)

Technical stuff

I’m not a weather nerd. The radiosonde is that package of instruments that’s hanging underneath the balloon in all those pictures you’ve seen.

They’re usually launched twice a day from various weather stations all over the country; an additional launch has been set up for tomorrow afternoon.

What the NHC is saying here is that they’re going to collect a huge amount of data, just like they did for Isaac earlier in the season when it threatened New Orleans. It made a tremendous difference then, and it will help now, too.

My guess is that they are trying to get a good idea, as early as possible, about how strong that atmospheric trough that’s crossing North America right now will be in several days as it approaches the East Coast and encounters ex-Sandy. As mentioned earlier, ex-Sandy should be pulled out to sea by a strong trough over the Central Atlantic, but if this second trough is strong enough, it could energize ex-Sandy and then pull the storm into the coast.

Bipolar?

I checked the 00Z model graphics before reading the NHC and Wunderground discussions and noticed something that has yet to be mentioned by either source.

CMC Oct 31 00Z run on Oct 24

October 31, per the CMC model. Ex-Sandy has gone “bipolar.” (Source)

You can click on images in these posts to make them larger.

The CMC model seems to show ex-Sandy splitting in two – that is, in this model run it’s going to respond to both troughs with part heading out to sea and part dropping in for a New England visit. The CMC is not mentioned in the NHC discussions, so I don’t know how reliable it is, but the 00Z GFS model might be hinting at something like that, too.

Well, whatever finally happens, there’s definitely going to be bad weather for the East Coast (and possibly inland a ways) around Hallowe’en. It might even get extreme. Be aware, and be safe.



Categories: Weather

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