Tag Archives: 2016 Atlantic Hurricane Season

Boom: Julia; Karl?

Update (Mid day Wed):

The disturbance in the eastern Atlantic is now a depression, and it is reasonably likely that it will be a named storm by mid day tomorrow, Thursday.

The predictions for the next several days do not have this storm turning into a hurricane any time soon; it should remain a storm or a depression, possibly going back and forth between the two, for four or five days, but after that, perhaps it will turn into something. Or not. Keep an eye on Karl, if this becomes Karl.

Meanwhile Julia is annoying people in the Southeast, but not doing much. However, keep an eye out for flooding.

Original Post:
There was a disturbance in the Atlantic. And it very suddenly developed the attributes to be a named tropical storm, so suddenly we have TS Julia hosing down the East Coast, on land already. That was fast.

And, farther out in the Atlantic, a zone of disturbance is reasonably likely, but by no means certain, to become a named tropical storm, and it would be called Karl.

Julia is my daughter, and Karl was my best friend in high school (he died soon after), so this is a big week for me wrt Atlantic storms! Not that you care, but for me it is cool.

What you might be more interested in is this: The total number of named storms for this time in the Atlantic is normally close to about 10, and with Karl, we’ll be at eleven with several weeks more to go. So, this is becoming a somewhat more active hurricane season than average, as predicted.

Ian is still out there somewhere.

The 2016 Atlantic Hurricane Season So Far. Keep an eye on Hermine.

A quick note about the current Atlantic hurricane season. With resect to just the US, we’ve had a fairly low level season, and it is easy to become complacent about this time, but in fact, the risks from Atlantic hurricanes rise about this time of year, so pay attention. Watch for Hermine. More on that below.

We are approximately in the middle of the 2016 Atlantic Hurricane Season, by calendar time. The number of named storms (tropical storms plus hurricanes) predicted for this year is about 14, taking the average of all the predictions made so far, and there have been 7 storms including one currently brewing in the middle of the Atlantic. So, perhaps we are right on track.

But, the first of those seven storms actually happened last year, but after the Hurricane Prediction Center had closed the book on the 2015 season, so Hurricane Alex got dumped into the 2016 season. (It happened in Janurary.) So, we are a bit behind in the total number of named storms.

But, we are not really half way through the hurricane season. It starts on June 1 and ends on November 30th, though as was the case with Alex, individual storms sometimes fail to get the memo. But, more importantly, the peak of the season tends to be around September 10th, and the distribution of Atlantic hurricanes over they year tends to be a bit skewed, with the latter half of the season being more active.

During the period 1851 to 2015 there were 1619 Atlantic tropical storms or hurricanes recorded. 609 of them happened prior to the end of August. The remaining 1010 happened in September, or later, with September and October having most of them.

So, roughly speaking, if we are half way to the predicted 14 named storms now and still in late august, one could guess that we’ll slightly exceed average expectations, but likely fall within the range of those expectations. We’d have to have over 20 or so named storms to raise the eyebrows of most of the predictors.

I get the impression that the percentage of named Atlantic storms that made landfall this year has been on the high side, though there has been no catastrophic landfall to date.

Katrina made landfall in about four days from now (in 2005). Among the deadliest, Sandy (which was a Hurricane that ate another storm and became too big and powerful to maintain its status as a hurricane by landfall, thus dubbed a “super storm” and enigmatically left off most hurricane lists) was later in the year, as were Stan, Jeanne, Mitch, Gordon, Fifi-Oriene, Flora, Jeremie, several other storms. Of recent deadly storms, Katrina was relatively early, and only 1979’s David came close (formed August 25th, fizzled out on September 8th).

So, speaking just of the more powerful storms, that is generally a phenomenon of September or October and now and then November.

Gaston is the currently active named storm. It is likely to form into a hurricane over the weekend, veer right before coming too close to Bermuda, and remain pretty far out in the Atlantic. There are no clear predictions of what it will do by mid week, but it is likely to weaken a bit on Wednesday. Gaston will be in hurricane-hostile territory at that time, so may be it will just go away.

Hermine is the name that would be given to what is now a tropical disturbance, should it form a tropical storm. The changes that it will do so are not small. If Hermine forms up into a reasonable storm, the chances that it would miss already-water-logged Florida are very small. I expect Hermine to be a significant weather event for the southern US.

The 2016 Atlantic Hurricane Season

This year’s Atlantic Hurricane season will be stronger, forecasts suggest, than that of the previous two years, and stronger than the average year.

The Atlantic Hurricane Seasons starts on June 1st. But, there was a hurricane that happened already, either late in last year’s season or very early in this year’s season, called Alex. That hurricane had to go somewhere, and I suppose the keepers of the records had already put their spreadsheet to bed when Alex came along on January 7th, so that storm gets counted as part of the season that will nominally start at the beginning of next month.

A lot of factors determine the number and strength (and path) of hurricanes in the Atlantic. One is sea surface temperatures. An El Niño in the Pacific tends to cause vertical wind shear, which attenuates hurricane formation. Saharan dust also reduces the chance of formation or strengthening of these storms. There may be an association with La Niña conditions and a stronger hurricane season.

A small number of agencies or groups put out their forecasts. Often, the forecasts are similar to each other, and typically they are reasonably accurate. One of the more famous groups comes out of Colorado State University and until his recent death, was led by Hurricane Expert William Gray. NOAA also puts out a forecast. The Earth System Science Center (ESSC) at Penn State has been issuing forecasts since 2007.

The following graphic shows the relationship between the median number of named storms predicted each year by those three sources and the actual number of named storms in the Atlantic.

Screen Shot 2016-05-12 at 2.07.29 PM

The first thing I notice is that the total range of variation in the predictions per year is less than the total range of variation in actual numbers over several years, and that the predictions roughly track the actual number of storms. This indicates that something is working. But I also note that the actual number of storms is often outside the range of predictions. So, while the predictions, in terms of number of named storms, give a reasonable estimate of the overall severity of the hurricane season, it is hard to predict these storms accurately months or weeks before the season starts.

This year, we are coming off an El Niño, which added surface heat to the already warm tropical seas, which of course is a result of human caused global warming. Also, we are probably heading into a La Niña season. If you look at the chart, you’ll notice that the last two seasons were relatively weak in the Atlantic. Last season’s El Niño and, probably, Saharan dust the season before, probably contributed to this.

This year, however, the two plotted forecasts (NOAA and ESSC) suggest a stronger season. There are two other forecasts, not shown on this graph, that also suggest a stronger season.

The average number of named storms for a base period of 1981-2010 is 12.1, so this year is predicted to be above average. The record high number of named storms was 28, in 2005 a year that also produced the record number of full-on hurricanes (15) and major hurricanes (7). That was the year of Katrina, Rita and Wilma, which were very memorable. (2005 was the year they ran out of names, remember?)

The ESSC report has, naturally more detail. From that report (emphasis added):

ESSC scientist Michael E. Mann, alumnus Michael Kozar, and researcher Sonya K. Miller have released their seasonal prediction for the 2016 North Atlantic hurricane season, which officially starts on June 1st and runs through November 30th.

The prediction is for 18.9 +/- 4.4 total named tropical cyclones, which corresponds to a range between 14 and 24 storms with a best estimate of 19 named storms. This prediction was made using the statistical model of Kozar et al. (2012, see PDF here). This statistical model builds upon the past work of Sabbatelli and Mann (2007, see PDF here) by considering a larger number of climate predictors and including corrections for the historical undercount of events (see footnotes).

The assumptions behind this forecast are (a) the persistence of current North Atlantic Main Development Region (MDR) sea surface temperature (SST) anomalies (0.88 °C in late-April 2016 from NOAA’s Coral Reef Watch) throughout the 2016 hurricane season, (b) development of a La Niña (Niño3 anomaly of -1°C) in the equatorial Pacific during boreal Fall/Winter 2016-17 (Climate Prediction Center April 2016 ENSO Discussion), and (c) climatological mean conditions for the North Atlantic Oscillation in Fall/Winter 2016-17.

If no La Niña develops (Niño3 anomaly between +/- 0.5 °C), then the prediction will be lower: 16.1 +/- 4.0 storms (range of 12-20 storms with a best guess of 16).

Using an alternative model that uses “relative” MDR SST (MDR SST with the average tropical mean SST subtracted) in place of MDR SST yields a slightly lower prediction (11.4 +/- 3.4 total named storms). This alternative model also includes the development of a La Niña.

So, as you can see, if there is no La Niñ this fall, there may be fewer storms in the Atlantic.