It’s the bomb

A friend asks “So what is up with this bomb cyclone term? Is it just a blizzard with a more compelling name? Or is it something unique that I have not experienced before now? Is bomb cyclone a technical term?”

Answer: like “polar vortex”, “bomb” is a term that has been used by meteorologists for many years but is just now being brought into popular usage by weather media. It refers to a winter storm over the ocean that strengthens very rapidly – the technical requirement is that the minimum surface pressure drops by at least 24 hectopascals (hPa, also known as millibars, or mb) in 24 hours. The term was brought into the scientific literature by Fred Sanders and John Gyakum in a 1980 paper, here:

http://journals.ametsoc.org/…/1520-0493(1980)108%3C1589%3AS…

a less technical and more recent discussion is here:

https://www.fastcompany.com/…/is-bomb-cyclone-even-a-real-t…

a bit more history and some quotes from Gyakum:

https://www.huffingtonpost.com/…/bomb-cyclone-definition_us…

And if you want to know more about the polar vortex while you’re at it: Darryn Waugh, Lorenzo Polvani and I wrote an article about that term for the Bulletin of the American Meteorological Society that is a bit more scientific than what you’ll find in the mass (or social) media, but more accessible than a typical peer-reviewed research article:

http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-15-00212.1

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The unbelievable coincidence of Cyclone Ockhi, Mumbai and me

On Monday evening, I will travel to Mumbai, India. I am going there for a research project in which we are trying to assess the risk that Mumbai might someday be hit by a tropical cyclone, particularly one strong enough to cause a significant storm surge and a major disaster for this low-lying coastal megacity. The problem is scientifically interesting – and difficult – precisely because such an event has not happened in modern history. So one can’t use historical data as a guide, although we know the risk is not zero – we believe that it has probably happened sometime, but it’s very rare our records are just not long enough. One has to use models of some kind to assess the risk, and our problem is to develop, evaluate, and use those models. (And climate change is most likely increasing the risk, but that’s another issue.)

Anyway, at this very moment there is a cyclone, named Ockhi, in the Arabian Sea. It is forecast to pass quite close to Mumbai on Tuesday evening, precisely when my flight (booked several weeks ago, and planned long before that) is due to arrive there!

ockhi_track_sunday_1130_est

While the storm is pretty powerful now, it is forecast to weaken a lot before landfall, so it will probably not cause a major disaster. And the models have it making landfall a bit to the north of Mumbai anyway (although with the uncertainty in the track forecast, a more direct hit is still possible). So this probably won’t be quite the disaster our project aims to address, but still, the coincidence is profoundly spooky. There are only 1-2 cyclones on average each year in the Arabian Sea, and most of those never come anywhere near this close to Mumbai. It’s an *extremely unusual* event, and it’s happening *precisely* as I’m coming to town to study it.

Harvey commentary

Some further commentary on Harvey. Mostly (but not all) about the climate connection.

Global Warming’s Role in Hurricane Harvey (The Takeaway, NPR)

Why Harvey’s devastation is so severe (CNN)

Climate Change Didn’t Cause Hurricane Harvey, but It Made It Worse (Fortune)

Commentary by Columbia Scholars (not just me)

Meanwhile, Hurricane Irma is breaking records and looking truly fearsome in the Atlantic.

December 2015’s crazy weather

I’m in Oregon, where December has broken rainfall records east of the Cascades, and the Cascades themselves are deep in snow. I got to see some of it up by Mt. Hood yesterday on a Christmas Day family cross-country ski outing.

hood_xmas_15

Though that was beautiful, I’m still sad to be missing the record-breaking warmth back east. (I like warm weather; it’s not an accident that most of my research over my career to date has been about tropical meteorology.) To help myself experience it vicariously, I wrote an op-ed piece for CNN about what the probable causes are. It has even been translated into Spanish.

Patricia’s ultra-fast intensification

I have a piece in CNN today about the incredibly fast jump that Hurricane Patricia made from tropical storm to what some people are saying should be called “category 7”. I point out that this case shows vividly why we need advances in the science of hurricane intensity prediction, at the same time as funding for this work was severely cut earlier this year. And, I compare Patricia to The Hulk.

Earlier, before landfall, Allison Wing and Chia-Ying Lee wrote an expert but accessible analysis of what the storm was doing and how the forecast models failed to capture it.

patricia-1530_custom-deef5f687ea6077b391eaa49719236b181dd7b05-s900-c85

Sudden excitement in the forecast

Update: Tropical Depression Eleven has already been upgraded and is now Tropical Storm Joaquin.

Some weather models shifted their predictions today from what they had been just before. Now New York City, along with much of the rest of the northeast US, is in the headlights of a weather event with some potential. We are now in the forecast cone of uncertainty of a tropical cyclone: currently it’s Tropical Depression Eleven, could intensify to become Tropical Storm Joaquin. Here is the track forecast map from the National Hurricane Center:

:210443W5_NL_sm

There is still quite a lot of uncertainty with this system, with the GFS model predicting it to be less likely than the ECMWF does that we’ll be hit by this storm. There are faint echoes of Sandy in that model disagreement – the EC predicted landfall earlier than GFS did then too. It doesn’t look like Eleven/Joaquin stands much chance of becoming an event of that magnitude, though, at least not as a wind or surge event (though never say never, or at least not yet).

There does seem to be good potential for heavy rain. Maybe very heavy, as tropical moisture funnels up from the south into a cold front that will be hanging around our region for a few days. NOAA’s precipitation forecast for the next five days puts over five inches of rain on a very large stretch of real estate from the Mid-Atlantic up to northern Maine:

p120i

Some model runs are producing numbers as high as double that – around ten inches – for NYC. This is perhaps unlikely, but possible.

The media is starting to pick up on this. Jason Samenow of the Capital Weather Gang has a nice summary; Weather.com has picked it up; and here is a local NYC TV take on it. From a quick scan, this coverage looks reasonable. It’s giving a sense of what the more extreme outcomes could be, while clearly stating that the uncertainties are still significant. This is as it should be. This is in the “stay tuned” category.