Record warmth in Atlantic Main Development Region for hurricanes

By: Dr. Jeff Masters , 4:52 PM GMT on March 08, 2010

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Sea Surface Temperatures (SSTs) in the Atlantic's Main Development Region for hurricanes were at their highest February level on record last month, according to an analysis of historical SST data from the UK Hadley Center. SST data goes back to 1850, though there is much missing data before 1910 and during WWI and WWII. The region between 10°N and 20°N, between the coast of Africa and Central America, is called the Main Development Region (MDR) because virtually all African waves originate in this region. These African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.)


Figure 1. The departure of sea surface temperature (SST) from average for March 7, 2010, as derived from the AMSR and AVHRR satellite data. Image credit: NOAA.

SSTs in the Main Development Region (10°N to 20°N and 20°W to 85°W) were an eye-opening 1.02°C above average during February. This easily beats the previous record of 0.83°C set in 1998. SSTs in the Main Development Region are already warmer than they were during June of last year, which is pretty remarkable, considering February is usually the coldest month of the year for SSTs in the North Atlantic. The 1.02°C anomaly is the 6th highest monthly SST anomaly for the MDR on record. The only other months with higher anomalies all occurred during 2005 (April, May, June, July, and September 2005 had anomalies of 1.06°C - 1.23°C).

What is responsible for the high SSTs?
Don't blame El Niño for the high Atlantic SSTs. El Niño is a warming of the Pacific waters near the Equator, and has no direct impact on Atlantic SSTs. Instead, blame the Arctic Oscillation (AO) or its close cousin, the North Atlantic Oscillation (NAO). The AO and NAO are climate patterns in the North Atlantic Ocean related to fluctuations in the difference of sea-level pressure between the Icelandic Low and the Azores-Bermuda High. They are some of the oldest known climate oscillations; seafaring Scandinavians described the pattern several centuries ago. Through east-west oscillation motions of the Icelandic Low and the Azores-Bermuda High, the AO/NAO controls the strength and direction of westerly winds and storm tracks across the North Atlantic. A large difference in the pressure between Iceland and the Azores (positive NAO) leads to increased westerly winds and mild and wet winters in Europe. Positive NAO conditions also cause the Icelandic Low to draw a stronger south-westerly flow of air over eastern North America, preventing Arctic air from plunging southward. In contrast, if the difference in sea-level pressure between Iceland and the Azores is small (negative NAO), westerly winds are suppressed, allowing Arctic air to spill southwards into eastern North America more readily. The winter of 2009 - 2010 has seen the most negative AO and NAO patterns since record keeping began in 1950, which caused a very cold winter in Florida and surrounding states. A negative AO/NAO implies a very weak Azores-Bermuda High, which reduces the trade winds circulating around the High. During December - February, trade winds between Africa and the Lesser Antilles Islands in the hurricane Main Development Region were 1 - 2 m/s (2.2 - 4.5 mph) below average (Figure 2). Slower trade winds mean less mixing of the surface waters with cooler waters down deep, plus less evaporational cooling of the surface water. As a result, the ocean has heated up significantly, relative to normal, over the winter. This heating is superimposed on the very warm global SSTs we've been seeing over the past decade, leading to the current record warmth. Global and Northern Hemisphere SSTs were the 2nd warmest on record in both December and January.


Figure 2. Sea level pressure averaged for the period December 2009 - February 2010 (left) and the sea level pressure averaged for the period December - February from the long-term mean (1968 - 1998). This winter, the Azores-Bermuda High was about 3 - 4 mb weaker than in a typical winter, due to strongly negative AO/NAO conditions. Image credit: NOAA/ESRL.


Figure 3. Departure of surface wind speed from average for December 2009 - February 2010. Winds were about 1 - 2 m/s (2.2 - 4.5 mph) lower than average over the Atlantic hurricane Main Development Region (MDR). Image credit: NOAA/ESRL.

What does this imply for the coming hurricane season?
According to Dr. Phil Klotzbach of the University of Colorado, February temperatures in the MDR are not strongly correlated with active hurricane seasons. The mathematical correlation between hurricane season Accumulated Cyclone Energy (ACE) and February SSTs is only 0.26, which is considered weak. Past hurricane seasons that had high February SST anomalies include 1998 (0.83°C anomaly), 2007 (0.71°C anomaly), and 1958 (0.68°C anomaly). These three years averaged 13 named storms, 8 hurricanes, and 3 intense hurricanes, which is considerably higher than the average of 10, 6, and 2. The big question is, how long will the strong negative AO/NAO conditions keep the Azores-Bermuda High weak? Well, the AO has risen to near-neutral values over the past week, and the latest 2-week forecast from the GFS model show that the AO and NAO will not be as strongly negative during March. This should allow the Azores-Bermuda High to strengthen some this month and increase the trade winds over the MDR. However, I still expect we'll set a record for warmest-ever March SSTs in the Main Development Region. Longer term, the crystal ball is very fuzzy, as our ability to predict the weather months in advance is poor. The long-range NOAA CFS model is predicting SSTs in the Atlantic MDR will be about 0.70°C above average during the peak months of hurricane season, making it one of the top five warmest years on record--but not as warm as the unbelievable Hurricane Season of 2005, which averaged 0.95°C above normal during August - October. The other big question is, when will El Niño fade? El Niño is currently holding steady at moderate intensity, and I expect that will continue through at least mid-April. It is possible El Niño will linger long enough into the year that it will create increased wind shear that will suppress this year's hurricane season.

Brazilian disturbance
An area of disturbed weather off the coast of Brazil, near 24S 36W, has changed little over the past two days. This disturbance still has a slight potential to develop into subtropical or tropical depression by Wednesday, according to the latest runs of the ECMWF, GFS, and NOGAPS models. Satellite imagery shows little organization to the cloud pattern, and only limited heavy thunderstorm activity. Wind shear over the region is about 20 knots, which is rather high, and should keep any development slow. Sea surface temperatures are about 27°C, about 1°C above average, which is warm enough to support a tropical storm. The system is small, limiting its potential to become a tropical cyclone. I don't think it will become a subtropical depression.

I'll have a new post on Wednesday.
Jeff Masters

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In all actuality, it is still way too early to predict with any precision what this season will bring us. Late April and May will give us a much better idea of what may come to pass.
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600. MTWX
That is why I love weather... All of the factors that come into play. All it take is one or two to be MIA to make or break a season
Member Since: July 20, 2009 Posts: 23 Comments: 1393
Quoting StormW:


LCD, Hi Def!


Prefer low def hurricane seasons personally.
Member Since: August 22, 2008 Posts: 12 Comments: 6010
I like those maps Storm! Not a lot of Fla. hits.
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Something ironic not really weather related, but it could be...if universal care passes, Rush Limbaugh will move to Costa Rica. Interesting, because Costa Rica has universal health care!
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Quoting MTWX:

don't know if I'm reading this graph correctly, but it seems that the '05 seson had about as much moisture as the last couple of seasons. If so how does that explain the high activity in '05 but not in '08 or '09?? Just curious...


Well obviously Sahel Rainfall is not the only factor that goes into an active season. There were other factors such as wind shear and SST that made 2005 triumph over '08 and '09. However, when you look at 2005 it didn't really have that great of a Cape Verde season, which could be partly attributed to the negative SRI:

Member Since: November 24, 2005 Posts: 635 Comments: 26594
Quoting PcolaDan:


So the remaining years are digital? ;)


LOL
Member Since: November 24, 2005 Posts: 635 Comments: 26594
593. xcool
Levi32 oh i haveing Accuweather Professional. tooo
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592. MTWX
Quoting Levi32:


We could see a net increase in Cape Verde activity for decades to come if the Sahel Rainfall cycle continues. This graph shows a clear multi-decadal trend of roughly 50 years since 1900, and we appear to be on the up-swing towards a more moist Sahel region, hence less dry air and more favorable conditions for tropical waves to develop over the eastern Atlantic.


don't know if I'm reading this graph correctly, but it seems that the '05 seson had about as much moisture as the last couple of seasons. If so how does that explain the high activity in '05 but not in '08 or '09?? Just curious...
Member Since: July 20, 2009 Posts: 23 Comments: 1393
Anyone in so. Fla. planning on buying a whole-home generator this season? If so, have you found any good deals?
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Quoting xcool:
Levi32 sorrying .Quoting Levi32:


Thanks Storm, I couldn't post the Accuweather image but I forgot about just writing out the values.????



The Accuweather Professional site has some nice CFS forecast graphics on it which include MSLP, but it's a site I have to pay for to use, so posting the images here could get me into copyright trouble. Storm uses the same site, and instead of posting the images he writes out the average pressure of the Bermuda High when someone asks about the CFS forecast.
Member Since: November 24, 2005 Posts: 635 Comments: 26594
588. xcool
w/b
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everyone also needs to remember to do their maint. on their generators. Don't want to wait till it's to late. And OLD fuel is BAD fuel.
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Quoting Levi32:


An analog year is a year that had similar conditions to what we have now. When we go back to history and look at how these years turned out with similar conditions to the present, it can provide great insight into what could happen now.

My analog package consists of the years 1958, 1964, 1966, 1970, 1978, 1995, 1998, 2005, and 2007. Storm likes 2003 more than I do lol. I'm just picky about the ONI, but 2003 can be in there too as an analog based on how that year turned out.


So the remaining years are digital? ;)
Member Since: August 22, 2008 Posts: 12 Comments: 6010
585. MTWX
I'm back.. what I miss
Member Since: July 20, 2009 Posts: 23 Comments: 1393
Finally...a return to about normal here in so. Fla.

Local Text Forecast for
West Palm Beach, FL (33409)

Mar 9 Tonight
Partly cloudy. Slight chance of a shower through the evening. Low around 60F. Winds ESE at 5 to 10 mph.
Mar 10 Tomorrow
Partly cloudy. High 78F. Winds SE at 15 to 25 mph.
Mar 10 Tomorrow night
Partly cloudy skies during the evening will give way to cloudy skies overnight. Low 67F. Winds SE at 10 to 20 mph.
Mar 11 Thursday
Afternoon showers and thunderstorms. Highs in the upper 70s and lows in the mid 60s.
Mar 12 Friday
Scattered thunderstorms. Highs in the upper 70s and lows in the low 60s.
Mar 13 Saturday
Scattered thunderstorms possible. Highs in the mid 70s and lows in the low 50s.
Mar 14 Sunday
Times of sun and clouds. Highs in the low 70s and lows in the upper 40s.
Mar 15 Monday
Times of sun and clouds. Highs in the low 70s and lows in the mid 50s.
Mar 16 Tuesday
Considerable cloudiness. Highs in the low 70s and lows in the mid 50s.
Mar 17 Wednesday
Chance of showers. Highs in the low 70s and lows in the mid 50s.
Mar 18 Thursday
Showers possible. Highs in the low 70s and lows in the mid 50s.
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583. xcool
Levi32 sorrying .Quoting Levi32:


Thanks Storm, I couldn't post the Accuweather image but I forgot about just writing out the values.????

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Quoting msgambler:
Good evening Levi, Storm. Great to see ya'll!! Hello everyone else


Evening Gambler :)
Member Since: November 24, 2005 Posts: 635 Comments: 26594
Quoting xcool:
. Levi32 what your try post Let's if i can help you .??


Forgive me but I didn't understand what you were trying to ask me lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26594
Good evening Levi, Storm. Great to see ya'll!! Hello everyone else
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Quoting plywoodstatenative:
what do you mean analog package?


An analog year is a year that had similar conditions to what we have now. When we go back to history and look at how these years turned out with similar conditions to the present, it can provide great insight into what could happen now.

My analog package consists of the years 1958, 1964, 1966, 1970, 1978, 1995, 1998, 2005, and 2007. Storm likes 2003 more than I do lol. I'm just picky about the ONI, but 2003 can be in there too as an analog based on how that year turned out.
Member Since: November 24, 2005 Posts: 635 Comments: 26594
577. xcool
. Levi32 what your try post Let's if i can help you .??
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when is this persistant trough thats been in place much of winter forecast to move?
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what do you mean analog package?
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Quoting plywoodstatenative:
basically the trof you refer to would be the ITCZ?


He means mid-latitude troughs that make hurricanes recurve. Cape Verde systems generally form further south than storms that form anywhere else in the Atlantic. Thus Cape Verde storms tend to track farther south and avoid getting recurved by upper troughs more often. Storms that form north of 20N like Storm said are more prone to getting recurved before reaching the United States.
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Quoting HadesGodWyvern:
555. nrtiwlnvragn 12:47 AM GMT on March 10, 2010
538. HadesGodWyvern

Thats the SOUTH AMERICA FORECAST DISCUSSION from HPC.

---
ya I saw that. The link is from the Brazil Meteorological Services blog though.


I saw that blog earlier, they must have updated it. Interesting read after I figured out to translate from Portuguese and not Spanish.
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Quoting plywoodstatenative:
Levi, I think you just made the entire blog take a deep breath


Lol, well they've known since February that I'm expecting an active season. I just hope it will spur people on to get prepared, as there are some nasty seasons in the analog package this year.
Member Since: November 24, 2005 Posts: 635 Comments: 26594
basically the trof you refer to would be the ITCZ?
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567. Skyepony (Mod)
Quoting Levi32:


Close, it was named after the state in which it made landfall, Santa Catarina.



For my struggle with geography that was pretty good.
Member Since: August 10, 2005 Posts: 162 Comments: 37810
Levi, I think you just made the entire blog take a deep breath
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Quoting plywoodstatenative:
So basically the PDO as you have described would lead into an active season. If thats the case, can you explain how it was that the freak season happened. Is that along the lines of what you have been talking or was that just an above average year of temperatures? If not, would that be somewhat of a model in a sense of what we might see this year or a worst case scenario for a season?


A cold PDO is always favorable for the Atlantic hurricane season, but winter analogs are a different beast. In my blog I pointed out some very interesting differences I found between the warm and cold PDO analogs.

As far as 2005, it is one of my analog years, although the El Nino during the '04-05 winter was weaker than the one we have now. However, the same general pattern of warm water in the deep tropics with cool to the north during the late winter existed as it does now, and 2005 had the same cool-biased neutral ENSO conditions during the summer that we expect this year. I don't think anyone can fully explain why 2005 had so many storms and other years didn't, but the same general conditions that made the years like 1995 and 2005 so active, are again present this year, so there is potential for a dangerous summer ahead.
Member Since: November 24, 2005 Posts: 635 Comments: 26594
563. HadesGodWyvern (Mod)
555. nrtiwlnvragn 12:47 AM GMT on March 10, 2010
538. HadesGodWyvern

Thats the SOUTH AMERICA FORECAST DISCUSSION from HPC.

---
ya I saw that. The link is from the Brazil Meteorological Services blog though.
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yeah I usually feel like digging a hole and jumping in it. For us not to get hit for at least four years in a row, is highly unusual and that tells me that this is going to be an interesting summer. And a crazy blog...
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560. HadesGodWyvern (Mod)
Seychelles Meteorological Services
Tropical Disturbance Advisory Number FOUR
DEPRESSION TROPICALE 13-20092010
4:00 AM Réunion March 10 2010
====================================

At 0:00 AM UTC, Tropical Depression 13R (1003 hPa) located at 20.3S 50.1E has 10 minute sustained winds of 28 knots with gusts of 43 knots. The depression is reported as moving west southwest at 4 knots.

Dvorak Intensity: T2.5

Near Gale-Force Winds
=====================
within the center in southern semi-circle

Forecast and Intensity
=====================
12 HRS: 20.4S 49.6E - 30 knots (Depression Tropicale)
24 HRS: 20.4S 48.9E - 35 knots (Tempête Tropicale Moderée)
48 HRS: 20.2S 48.5E - (Depression sur terre)

Additional Information
=======================
Convection remains alway quite fluctuating, but seems to organize into curved band pattern. System slowly moves now generally west southwestward towards Malagasy eastern coast. Over the next 24 hrs, environmental conditions are rather good with improved low level tradewinds inflow and no wind shear and good divergence under upper level high pressures. System could reach the moderate tropical storm stage. System should go on tracking westward under the steering influence of low and mid level highs. Landfall is expected between 24-36 hrs over the Malagasy coast.
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Now I feel like bringing you down to South Florida during the season, instead of you being up there in Alaska.
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So basically the PDO as you have described would lead into an active season. If thats the case, can you explain how it was that the freak season happened. Is that along the lines of what you have been talking or was that just an above average year of temperatures? If not, would that be somewhat of a model in a sense of what we might see this year or a worst case scenario for a season?
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Quoting plywoodstatenative:
Hey Levi, did you really have to ruin my week...


I'm sorry =/

It's better to warn you guys about the danger to come then to remain silent and have some people not prepared. Everyone should be fully prepared every year anyway, but some are more prompted to when they know a bad season may be coming.
Member Since: November 24, 2005 Posts: 635 Comments: 26594
Hey Levi, did you really have to ruin my week...
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538. HadesGodWyvern

Thats the SOUTH AMERICA FORECAST DISCUSSION from HPC.
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storm what is the correlation between low surface pressures and the strength of the Bermuda High. Basically what I am asking, is what does all that combined with the CV season mean for the East Coast for hurricane season?
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Quoting plywoodstatenative:
One last item before I go back into blog hibernation till the season starts. I was reading a local paper recently, the talk was that we are looking at a Neutral La Nina year, whats the tendency after having a very cold winter to then have a neutral year in the way of El Nino or La Nina? Does the unusually long winter have any impact on what our season will be like; The way the Jetstream is set up, whats the talk as to whether that type of set up will be around for the remainder of spring into summer?


I discuss this in some detail when I talk about analog years in my 2010 Atlantic Hurricane Season Outlook, but in a nutshell it varies. In my set of analog years for this hurricane season, all the preceding winters during a cold PDO were similar to this winter, very cold in the southeast USA. During a warm PDO the preceding winters were all warmer than normal in the southeast USA. We are entering a cold PDO now, so you could say it agrees with the cold PDO analogs better, but winter correlation with the following hurricane season is complicated and less than perfect.

That said, having a strong El Nino this winter that is now dying as we head into the summer is the most favorable case for an active Atlantic hurricane season, because it leaves excess heat in the atmosphere and oceans around the tropics. The ensuing neutral or La Nina conditions provide a more favorable atmospheric environment over the Atlantic, which, combined with all the heat available, can make for a dangerous season.
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They may not be able to name it since a name list does not exist, but according to the data they should number it SL012010.

SL 90 2010031000 BEST 0 298S 482W 35 1003 LO


SL 90 201003092345 2980S 4810W SAB 2525 /////
SL 90 201003092345 2980S 4820W TAFB 2525 /////

ST2.5 from both SAB and TAFB
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.