Dan's Wild Wild Science Journal

I have had a TON of questions about the impact of a Gulf hurricane on the oil slick. The short answer to this is nobody really knows. NOAA has a short document out that covers the questions and what little IS known.

Good science here:

Click for the pdf.

More soon…

In my last post I gave some of the reasons I thought we would see a very active hurricane season. Here is what the NOAA folks think. They released their forecast for the 2010 season today.

As I expected it looks like it will be a mean year. Possibly one of the all time most active years. Here are NOAA’s numbers:

An 85% chance of an above normal season.

A 70% probability for each of the following ranges of activity this season:

• 14-23 Named Storms,
• 8-14 Hurricanes
• 3-7 Major Hurricanes
• An ACE range of 155%-270% of the median.

From NOAA/TPC

The ACE stands for Accumulated Cyclone Energy Index (Developed by NOAA).  It’s a measure of the total amount of energy from all the storms in a particular season. (In the same basin) NOAA’s official definition: The ACE index is a wind energy index, defined as the sum of the squares of the maximum sustained surface wind speed (knots) measured every six hours for all named systems while they are at least tropical storm strength.

An average year brings about 6 hurricanes and 10 tropical storms. So this is a forecast of a possible hyperactive season.

Could we still see a normal season?

Yes!

El Nino may linger and wind shear may not be as weak in the tropical Atlantic as forecasted. The odds are heavily against those things happening though.

For more on the reasons why see my previous post.

From NOAA- The El Nino is fading away in the Pacific but Atlantic sea surface temps. are near record levels. Both of these factors argue for an active hurricane season in the Atlantic.

Hurricane season begins June 1st and NOAA’s hurricane experts will release their 2010 season forecast Friday 28 May. It’s not much of a secret among meteorologists what it will be.

Likely BAD.

Actually Daffy, it's HURRICANE Season. (Warner Bros.)

Forecasting the number of hurricanes we will see each year is a very tricky project. There is some skill but changes in the sea surface temperatures and in the upper level wind shear during the summer months make any forecast iffy.

So, that said here is why NOAA will forecast an increased number of hurricanes this year.

THE AMO:

The Atlantic Multi-Decadal Oscillation is an ocean atmosphere oscillation that runs in 10-30 year cycles. It causes warmer than normal waters in the main development region and favorable winds for more hurricanes. (On top of changes caused by increasing greenhouse gases). The AMO cycle has been favorable for above average hurricane seasons since the mid 1990′s.

Models are forecasting El Nino to quickly die and an increasing possibility of a La Nina. La Nina's cause more hurricanes. Just the opposite of El Nino's.

EL NINO:

Last winter’s El Nino is now rapidly disappearing. The warmer than normal waters in the Equatorial Pacific have almost disappeared and virtually all of the models are forecasting a return to either neutral or even La Nina conditions by the end of summer.

El Nino’s in the Pacific produce a weather pattern in the Atlantic that causes increased wind shear. This usually means fewer hurricanes. La Nina’s produce lower wind shear in the Atlantic and are associated with more active seasons.

SEA SURFACE TEMPS:

The oceans worldwide are the warmest ever measured right now. There are very strong indications this is due to the increasing greenhouse gases in the atmosphere. The record warmth in the Atlantic is likely caused the AMO discussed above and the Arctic Oscillation.

This is the same pattern of atmospheric pressure that was responsible for the cold and snowy winter in the UK and the Eastern USA. It also causes warm waters to spread over the main development region for hurricanes in the Atlantic.

You add up all of this and you get very good odds for an active season. Keep in mind that the Arctic Oscillation may change and sea water temps could cool. El Nino may hang on longer than expected too. If this happens we could see a normal season, or even below.

The odds however say otherwise.

Dan

PS There is some fascinating new science in one of the great questions of meteorology. Will we see more or fewer hurricanes in the warmer World of the late 21st century?? I will have that post soon. I’m still reading the papers…

This TED talk by coral reef expert Jeremy Jackson is  a must watch state of the oceans.

With the oil spill in the Gulf making news, it’s especially apropos.

A lot of tropical news this week. The 2009 hurricane season in the Atlantic has stirred to life quickly with two (Update Sunday: 3 !) tropical storms forming on Saturday. It’s not at all unusual to have little hurricane activity until August. The season runs from June 1st to November 30, but the prime season is from Aug, 1st to mid September. American forecasters have an old saying that there will almost always be a hurricane on the weather maps when Labour Day arrives.

From NOAA/NCDC. The bigger the dot the more the temperature was warmer or colder than normal.

These storms form in very warm ocean. The National Climate Data Center (NOAA) released the July global land and ocean temperatures on Saturday. Ocean temps were the warmest on record for July. The land and ocean temps were the 5th warmest on the instrumental record. This follows June 2009 which also came in as warmest.

Another interesting bit of tropical news this week is a new paper published in Nature on hurricanes of the past. One of the great debates in science right now is the question of whether climate change will bring more hurricanes or fewer. The debate has raged between two opposing groups. Kerry Emanuel of MIT has produced interesting evidence that we have seen an increase in hurricanes already due to the warming of the past 50 years.

Chris Landsea of NOAA has produced evidence that we are just detecting more tropical storms, and that there has not been an increase. I had a chance a couple of years ago to hear both of them present at the AMS meeting in San Antonio. I left with the firm conviction that the question remains open. Understand here, that this debate is not about climate change in general. Despite what you read on the Internet, science has moved on from that.

One thing that does seem very certain now is that hurricanes in the warmer world of late this century, will be wetter. Perhaps considerably wetter. The kind of catastrophic flooding we saw in Taiwan this past week, will likely be more common in the future.

Why you ask? Water vapour.

GOES Image of Tropical Storm Bill Early Sunday. from NASA MSFC

If the average temperature of the air over the oceans rises 1 degree F, the air can hold 4% more water. (This is one reason why more snow is likely in Antarctica as it warms, not less. A 3C rise in temp. by late this century would bring an increase of around 22% in the amount of water held in the atmosphere! (You won’t see that bit of science on these junk science sites)

Sea surface temperatures are a major factor in hurricane formation. If the sea surface temperature is below about 27C then hurricanes are not likely. Upper level wind shear and atmospheric water vapour are other important ingredients.

Other factors like wind shear in the upper atmosphere act to inhibit hurricanes. The El Nino that develops every 4-7 years in the Pacific, increases the wind shear over the Atlantic, and we usually see fewer storms. Will there be more wind shear in a warmer world? Possibly. Conditions could combine to produce about the same number of storms in the future. (Much wetter ones though)

Micheal Mann of Penn State University is the lead author of a fascinating paper in this weeks NATURE. His team used soil/silt cores in a series of locations to estimate past hurricanes. If a hurricane hits a coastline, the overwash of sea water will leave a deposit that can be identified in the cores. They used these sediment cores to estimate hurricane activity over the last 1500 years. In addition, they used a statistical model that factored in variables like sea surface temperature to estimate storms as well.

Reconstruction of landfalling Atlantic hurricanes. Nature 460, 880-883 (13 August 2009) | doi:10.1038/nature08219; Atlantic hurricanes and climate over the past 1,500 years Michael E. Mann, Jonathan D. Woodruff2 et al

They found that during a period of rather warm Atlantic Ocean water around 1000 years ago, we saw as many hurricanes as we have over the past 15 years. This is a good confirmation that warmer seas, do give more hurricanes and perhaps more intense ones.

Chris Landsea of NOAA argues that the increase in storms over the past century is just an artifact of spotting them more easily with satellites and aircraft. One thing seems likely here, the hurricanes did increase in the past during a period of warmer oceans.

Whether or not a warmer world caused by human means, instead of natural ones, will do the same is still open for debate. The science, however, might just be beginning to tilt in favor of Mann and Emanuel.

Either way, with sea level now rising 3mm per year, and increasing, future hurricanes, will be wetter and cause more destruction. The current thinking is the IPCC will be adjusting their forecast of sea level rise up considerably in the next report.

This back and forth in the peer reviewed literature is how science advances. When we can answer the question of hurricanes in a warmer world, we will have gleamed another piece of fundamental knowledge of how are planet works.

I end with a book recommendation. Kerry Emanuel of MIT is one of the leading experts on hurricanes. He has written a fabulous book called Divine Wind. It combines poetry and science. It’s one of the best general audience  science books ever written.

Note this is a dual post- I wrote it as a guest post on Skywarn 256′s Weather Blog as well.