Thursday, November 6, 2014

The Explosive Extratropical Transition of Nuri

Former super typhoon Nuri is currently sitting off the coast of Japan and was recently downgraded from a typhoon to a tropical cyclone.  Nuri will have the good fortune, however, of experiencing resurrection as it is currently undergoing extratropical transition, the transition from a tropical into an extratropical cyclone, and is forecast to undergo explosive development as it moves northward toward the Bering Sea.

Below is a look of the entire process from 1200 UTC 4 November through 0000 UTC 10 November based observations and the 0600 UTC GFS.

The forecast minimum central pressure of somewhere between 920 and 924 mb is reached at 0300 UTC 8 November.  Based on the lowest contour, Nuri deepens an incredible 64 mb in the 24 hours preceding this forecast time.  Meteorologists call such development explosive and sometimes call storms of this type bombs.

Here's a view of the forecast cloud structure of the storm at 1500 UTC 8 November when it has coiled up nicely. Not bad for a relatively low resolution numerical model with output on a 0.5ºx0.5º latitude–longitude grid.  

Weather historian Christopher Burt had a very nice post a few years ago discussing "superextratropical" storms in Alaska and sea level pressure records that I encourage you to take a look at to put Nuri into context.  He states that the deepest extratropical cyclone observed had a central pressure of 913 mb and the deepest extratropical cyclone to affect Alaska had a central pressure of 925 mb.  If the most recent forecasts hold, Nuri will be way out on the long, skinny tail of the cyclone distribution and in there with the deepest of the deep.   

Nuri also provides an example of just how far that our field has come in the last three decades.  In the 1980s, two major field programs, the Genesis of Atlantic Lows Experiment (GALE) and the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) to help understand and improve the prediction of major extratropical cyclones.  At the time, the storms were poorly predicted and anticipated, and a major threat to lives and property on the high seas.  Today, computer models provide forecasts of such storms days in advance, allowing for the rerouting of ships and other preparations.  There is still more work to be done, but we have come a long ways when it comes to predicting these storms.     


  1. A beautiful storm. let's pull it in to the Intermountain West, please!

  2. Wow! yeah you forgot to mention how this bomb is going to come bomb our high pressure away.....for good.

  3. Curious as to whether this will affect Utah's weather?

    1. No direct effects. However, the extratropical transition of Nuri sets off a sequence of events that ultimately leads to the development of a pronounced block over northwest Canada and Alaska. That block will contribute to a series of cold surges down the east side of the Rockies next week. We will probably see some cooling early next week, and could flirt with canyon winds at times, but no major storms through at Wednesday. After that we'll have to see.

  4. Well looks like the GFS perked up this morning...finally, lets hope it holds!