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Dorian is a TSINO; Flossie nears Hawaii

July 27th, 2013 - 12:37 am

The National Hurricane Center has officially maintained Dorian’s status as a 40 mph tropical storm as of 11pm EDT. But, my fellow Americans, let me be clear: Dorian is a TSINO (Tropical Storm In Name Only).

Here’s another view of the ASCAT pass. Dorian has also looked horrible all day on satellite, and NOAA’s Satellite Services Division deemed it “too weak” to run the “Dvorak” analysis that’s used to estimate tropical cyclone strength. “Not sure I’ve seen that before with an active ‘tropical storm’,” writes Charles Fenwick.

The NHC’s 11pm advisory makes Dorian’s “TSINO” status pretty clear. The headline on the public advisory is “DORIAN FORECAST TO BECOME A REMNANT LOW IN A DAY OR SO.” From the discussion:

DORIAN…HAS BEEN DEVOID OF DEEP CONVECTION FOR SEVERAL HOURS. I WAS TEMPTED TO DECLARE DORIAN A REMNANT LOW IN THIS ADVISORY…BUT GIVEN THE FACT THAT THE CIRCULATION IS MOVING OVER WARMER WATERS AND SHEAR IS FORECAST TO LESSEN…NEW CONVECTION COULD REDEVELOP. THE BEST OPTION IS TO KEEP THE CYCLONE FOR A COUPLE OF MORE ADVISORY CYCLES AND MONITOR THE EVOLUTION OF THE CONVECTION.

Translating from NHC-ology into English: “It’s not actually a tropical cyclone right now, but we’ll maintain it as a minimal T.S. for now, just in case it redevelops overnight.”

That said, it’s possible that a flare-up of thunderstorm convection in the last few hours could extend Dorian’s official life by a few more advisories, notwithstanding the lack of a closed circulation (which is ostensibly the dividing line between “tropical cyclone” and “tropical wave”). It’s the Monty Python storm!

As Fenwick explains, there’s precedent for ignoring the lack of a closed circulation and keeping alive a seemingly-dead storm when a potential for future reorganization beckons:

It is memories of…[2005's] Irene…that caused me to express a bias towards Dorian persisting. Irene was quite the survivor of shear & dry air, going down to a tropical depression and having “little to no evidence” of a closed circulation at one point, before finally finding more hospitable conditions and eventually becoming a hurricane. The discussions from the 7th through the 11th make for fun reading. Note how it was never forecast to die despite (apparently) utterly failing to meet the criteria for a tropical cyclone at one point.

Now, my recalling of 2005 Irene isn’t to suggest that we are certainly in line for a repeat, it’s just to offer a reminder that a circulation can manage to survive in arduous conditions. A spark of convection here and there and it can survive near death. As the 11 PM discussion noted, should a circulation survive and should it avoid land, there is a promised land ~ 3 days out. That’s the rationale for the thinking that makes this aspect of NHC-ology, a storm being kept alive past its apparent due date, exist. It’s not 100% nuts, just, you know, kind of nuts, at times.

Another 2005 storm which went a step further, actually dying out, and then still managed to come back once it reached a “promised land”: Tropical Depression Ten, which died out near the northern Lesser Antilles on August 14, only to combine with another tropical wave nine days later to form a cyclone you may have heard of: Katrina. Like Fenwick, I’m not suggesting in any way that we’ll see a repeat of that — it’s just a memorable proof of concept.

However, the more significant threat to the U.S. — albeit still a fairly minor one — comes from the Pacific’s Tropical Storm Flossie (yes, “Flossie”), currently with 60 mph winds, which is expected to reach the Big Island of Hawaii late Monday or early Tuesday as either a weak tropical storm or a tropical depression:

Flossie has cold waters and wind shear ahead, which will cause inevitable weakening, as nearly always happens with storms approaching Hawaii from due east (rather than recurving up from the south, Iniki-style). But for now, Flossie certainly looks much more fearsome than Dorian:

Wind impacts should be mild, but flooding is possible in Hawaii from Flossie’s rains.

I may or may not update Weather Nerd over the weekend, depending on what happens with Dorian and Flossie, but regardless, for more frequent updates, follow me on Twitter (@brendanloy). Also, as I always say, Amy Sweezey’s “Wx Tweeps” Twitter list is good for getting the latest info.

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