2014 Atlantic hurricane season outlook

By: TropicalAnalystwx13 , 1:59 AM GMT on April 21, 2014

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First off, Happy Easter to all reading this.

It's a nice day out today. The sun is shining, the air is warm, the birds are chirping, and the bees are busy pollinating. Oh wait, just kidding, it's pouring down rain with gusts over 45 mph here; my yard is a swamp. Must be spring in southeastern North Carolina. With that said, we are quickly approaching the official June 1 start of the 2014 Atlantic hurricane season, and we're doing so on the heels of one of the biggest busts the meteorological community has ever seen after the events of last season. 2013 is a good example of how meteorology is an inexact science; it should be realized that any forecast from any individual or any organization should not be expected to turn out with 100% accuracy.

When dealing with seasonal forecasts, it's usually best to start with the largest contributor to activity...in this case, the Pacific Ocean. A first glance at the sea surface temperature anomaly map reveals a very different pattern than we've been accustomed to the past few years. The Pacific Decadal Oscillation (PDO) - an index used to describe the sea surface temperature configuration in the north Pacific north of 20°N - has been running positive since the start of 2014, conflicting the overall negative phase that began in earnest in 2007. A positive PDO features warmer-than-average waters stretching from the Aleutian Islands to the coastline of California to the Hawaiian islands, with cooler-than-average waters east of Japan. In a negative PDO, the anomalies are reversed. In addition, we notice a notably warmer equatorial Pacific compared to the stretch of cool Neutral or La Niña conditions that began in 2010.


Figure 1. Global sea surface temperature anomaly map (based on 1982-2010 climatology). Image credit to Levi Cowan of Tropical Tidbits.

There has been a lot of media attention the past few months towards the potential development of an El Niño event by summer 2014. An El Niño is a band of anomalously warm waters stretching from the northwestern coastline of South America into the central Pacific. This configuration leads to extreme changes in the global weather pattern, with warmth and drought conditions usually found across The Philippines, Indeonesia (and surrounding locations), northeastern South America, and Australia, and cooler and wetter conditions across the southern United States. El Niños typically lead to a spike in global temperatures, and this evidenced by the fact that the last two significant events...the 1997-98 and 2009-10 El Niños...both made the latter years among the warmest on record.

If we take a look at model projections for this likely El Niño, we see that there is some discrepancy as to how strong it becomes. The Climate Prediction Center/International Research Institute model suite is generally the most conservative (as is typical) with this upcoming event, showing a peak just above 1C. Meanwhile, the mid-April update of the ECMWF ensembles is more bullish, showing a peak near 1.5C. The CFSv2 forecasts a peak near 2C. Depending on the values, the potential El Niño can be broken down into categories: if the peak tri-monthly Niño 3.4 value falls on or between 0.5-0.9C, it can be classified as weak; if the value falls on or between 1-1.4C, it can be classified as moderate; if the value falls on or between 1.4-1.9C, it can be classified as strong. Finally, though this term is not official, it is widely used--if the value falls on or above 2C, the El Niño can be classified as super. Only the 1982-83 and 1997-98 El Niños have observed an Oceanic Niño Index (ONI; tri-monthly Niño 3.4 value mean) in this category. Given model projections and the current state of the ENSO, I feel it is almost certain that we see an El Niño event of any magnitude; a high chance that we see an El Niño event of moderate strength; a medium chance that we see an El Niño event of strong strength; and a medium chance that we see an El Niño event of super strength.


Figure 2. The IRI/CPC ENSO model suite from mid-April 2014. Image credit to the Climate Prediction Center and International Research Institute for Climate and Society.

Breaking down the current state of the ENSO, we can see that easterly winds have dominated the equatorial Pacific for the past few weeks. This is in contrast to the January-March period, which featured mainly westerly winds. Easterly winds are associated with stronger trade winds and more upwelling (cooler waters), while westerly winds are associated with reduced trade winds and less upwelling (warmer waters). This change has caused many people to second guess their predictions of an El Niño event, but overall, this is just "a drop in the pond". If we take a look at the CFSv2 forecast for the next month, we see that it shows a renewal in westerly winds across the equatorial Pacific for this upcoming week, lasting through the middle portions of May. This is in response to a strong pulse of the Madden-Julian Oscillation currently moving west to east across the western Pacific Ocean. The MJO is associated with westerly wind bursts along the equatorial Pacific, leading to overall warming. Low-latitude tropical cyclones...usually within 5N of the equator...can also produce westerly wind bursts.



Figure 3. CFSv2 forecast for 850mb winds for weeks 1-2 (left; 20 April-3 May) and weeks 3-4 (right; 4-17 May). Image credit to the Climate Prediction Center.

As a consequence of the first westerly wind burst in January, a downwelling oceanic kelvin wave was initiated and has since spread eastward across the equatorial Pacific Ocean. In response to this, an incredible amount of warm water has built near 150 meters, with anomalies of 6-7C above average visible on the latest Climate Prediction Center update. This is the strongest subsurface warm pool we've ever seen prior to the formation of an El Niño, and much stronger than the subsurface warm pool of 1997 at this time. This subsurface warm pool in itself won't lead to an El Niño of strong to historic proportions as we saw in 1997-98...continued tropical forcing is needed for that...but it does significantly increase our chances are seeing at least a moderate El Niño event.


Figure 4. Equatorial Pacific temperature anomaly map as of April 13, 2014. Image credit to the Climate Prediction Center.

At this point, some may be wondering why El Niño matters with regards to Atlantic hurricane activity. In an El Niño, warmer waters along the equatorial Pacific warm the air just above the surface. Because warm air is less dense than cool air, the air rises and expands, leading to showers and thunderstorms. The resultant outflow from these disturbances fans out, leading to increased wind shear across most of the Gulf of Mexico and Caribbean Sea. In addition, a stronger-than-average subtropical jet stream favors above-average wind shear across much of the aforementioned regions. Wind shear tilts the circulation of a developing tropical cyclone in addition to removing heat/moisture needed for the formation of a system. El Niños go hand-in-hand with above-average sea level pressures across the Atlantic, as indicated by the latest forecast from the ECMWF:


Figure 5. Mid-April ECMWF forecast of mean sea level pressure for the August-September-October 2014 period. Image credit to the European Centre for Medium-Range Weather Forecasts.

Now viewing a sea surface temperature anomaly map of solely the Atlantic Ocean, we notice that the basin also looks much different than the configuration we've become so accustomed to. While warm waters encompass much of the northwestern Atlantic, near-average to below-average waters are observed across the north-central, central, and eastern Atlantic: this is a negative Atlantic Multidecadal Oscillation (AMO) pattern. Because the eastern and central Atlantic are the birthplace for Cape Verde hurricanes - which make up a majority of the longest-lasting and strongest hurricanes in the Atlantic - this is not a favorable configuration for Atlantic hurricane activity. This pattern has been brought about by a strongly positive North Atlantic Oscillation (NAO) during the winter and early spring months. In a positive NAO, a stronger-than-average Bermuda High promotes stronger-than-average trade winds across most of the tropical Atlantic, leading to evaporational cooling of the water. If we take a look at the forecasts, we see that while the NAO is forecast to go negative for a brief period of time in late April, the majority of available models show a similar ocean temperature configuration lasting through the fall of 2014.


Figure 6. Atlantic sea surface temperature anomaly map. Image credit to Levi Cowan of Tropical Tidbits.

Other than the aforementioned factors, there are a few things to watch out for as we progress into this season. Vertical instability in the tropical Atlantic continues well below-average, as has been the case for the past few years. While this factor may not limit the number of named storms, it does limit the intensity of tropical cyclones that form; will its trend continue in the season? Meanwhile, we are beginning to transition from a period of below-average rainfall across the Sahel to one that features wetter-than-average conditions. A wet Sahel is correlated to stronger-than-average tropical waves that have a higher probability of developing once over the ocean. Despite cooler waters and increased shear, will the Cape Verde season be completely dead this year? In the Indian Ocean, sea surface temperatures are slightly above-normal, indicating a neutral to slightly positive Indian Ocean Dipole (IOD). A positive IOD is associated with a weaker western Africa monsoon circulation, and is unfavorable towards tropical activity in the eastern Atlantic as seen in 2007 and 2011. Finally, the Gulf of Guinea has been generally above-average this year, contrasting the generally cool waters that have existed there during the past few seasons. In years with a cool Gulf of Guinea, the Intertropical Convergence Zone (ITCZ) was shifted farther north and allowed for stronger-than-average tropical waves to form within the African Easterly Jet. Will we see a cooldown before the start of the season?


Figure 7. Timeseries of Sahel rainfall anomalies from 1900 to 2013.

Given the current state of the Pacific and Atlantic, as well as model projections, we can choose a set of analog years from the database. In doing so, I chose years that came on the heels of an extended period without an El Niño but at the same time entered an El Niño of at least moderate intensity, all the while maintaining cooler-than-average tropical Atlantic sea surface temperatures (mainly negative AMO years). The list is as follows: 1963, 1968, 1972, 1982, 1991, 1997, 2002, and 2009. If we take the mean of these years, we come up with 8.375 named storms, 3.75 hurricanes, 1.25 major hurricanes, and an Accumulated Cyclone Energy (ACE) index of 50.5 units. Given the possibility that the El Niño comes on sooner than many of the listed years and also peaks higher than the listed years, my forecast calls for 7-9 named storms, 1-3 hurricanes, 0-2 major hurricanes, and an ACE index of 35-55 units (roughly 40-60% of average). An interesting tidbit to note is that the focus of tracks during these analog years encompassed the extreme northern Gulf Coast and the Southeast United States. While every individual living along any stretch of coastline that borders the North Atlantic should be prepared during any season, this area may need to keep an extra eye to the tropics during the season. For more information about track congregation during moderate El Niño years, watch Levi Cowan's 2014 Atlantic hurricane season outlook video. As is emphasized every year, significant storms - such as Andrew during the 1992 Atlantic hurricane season - can still occur during an otherwise dead season.

TropicalAnalystwx13

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28. WunderAlertBot (Admin)
5:06 AM GMT on May 31, 2014
TropicalAnalystwx13 has created a new entry.
27. drs2008
2:39 PM GMT on April 24, 2014
I believe that last years bust has affected this years prediction numbers. Meteorology = inexact science.Human bias. At this time we are missing a few variables. Perhaps sunspot cycles.
Member Since: July 4, 2008 Posts: 1 Comments: 197
26. StormTrackerScott
2:25 AM GMT on April 22, 2014
Member Since: February 28, 2013 Posts: 9 Comments: 4768
25. StormTrackerScott
2:22 AM GMT on April 22, 2014

That deep blob of warm water is about 300 feet deep and the size of the USA. That deep warm water is being pushed east due to the reversal of the trade winds and it’s moving towards the surface. When that warm water meets the surface, it’ll interact with the air in the atmosphere warming it up and modifying weather patterns.
Member Since: February 28, 2013 Posts: 9 Comments: 4768
24. Astrometeor
12:42 AM GMT on April 22, 2014
Quoting TropicalAnalystwx13:

Link


Yay! Thanks Cody.
Member Since: July 2, 2012 Posts: 101 Comments: 10500
23. TropicalAnalystwx13
6:23 PM GMT on April 21, 2014
Quoting 20. Astrometeor:

Hi Cody.

I have a question about Wikipedia. In its entry for Hurricane Bob of 1991, Wiki states this:
In addition, seventeen fatalities were reported in association with Bob. However, on the side-bar with the data about Bob, the entry states Fatalities 309 direct, 2 indirect.

I would assume the 17 number is correct, given the table charting the death toll later on in the article.

#finding-errors-in-Wiki's-tropical-section-since- 2013.

:)

Edit: Link to Bob in case you need it.

Link
Member Since: July 6, 2010 Posts: 113 Comments: 32863
22. Astrometeor
5:58 PM GMT on April 21, 2014
Not wanting to answer for Cody, but...

Quoting Tropicsweatherpr:
Very good analysis Cody. What are your analog years?


Taken from his blog: The list is as follows: 1963, 1968, 1972, 1982, 1991, 1997, 2002, and 2009.
Member Since: July 2, 2012 Posts: 101 Comments: 10500
21. Tropicsweatherpr
5:36 PM GMT on April 21, 2014
Very good analysis Cody. What are your analog years?
Member Since: April 29, 2009 Posts: 75 Comments: 14916
20. Astrometeor
5:32 PM GMT on April 21, 2014
Hi Cody.

I have a question about Wikipedia. In its entry for Hurricane Bob of 1991, Wiki states this:
In addition, seventeen fatalities were reported in association with Bob. However, on the side-bar with the data about Bob, the entry states Fatalities 309 direct, 2 indirect.

I would assume the 17 number is correct, given the table charting the death toll later on in the article.

#finding-errors-in-Wiki's-tropical-section-since- 2013.

:)

Edit: Link to Bob in case you need it.
Member Since: July 2, 2012 Posts: 101 Comments: 10500
19. MAweatherboy1
10:23 AM GMT on April 21, 2014
Thanks Cody, very good discussion. Your numbers are close to mine.
Member Since: February 11, 2012 Posts: 84 Comments: 8047
18. BaltimoreBrian
4:20 AM GMT on April 21, 2014
Sounds like Cody is forecasting a generally weak season with homegrown storms. Agnes was in 1972, a big bloated wet thing, and very destructive. Danny in 1997 caused a lot of problems for the Gulf Coast. Marco in 1991 caused extensive flooding in the southeast, Bob gave New England a hard slap and there was the 1991 Halloween storm. Flora in 1963 was very destructive in the Caribbean. As always, we'll need to keep an eye out.
Member Since: August 9, 2011 Posts: 26 Comments: 8918
17. nigel20
4:20 AM GMT on April 21, 2014
Thanks for the in-depth blog post, Cody. Very impressive! :)
Member Since: November 6, 2010 Posts: 12 Comments: 8488
16. Barefootontherocks
4:07 AM GMT on April 21, 2014
Wow. Very excellent. Not sure how something can be a superlative of excellent, but this blog is!
Clear. Understood.

Thanks, TA13.
Happy Easter
Member Since: April 29, 2006 Posts: 159 Comments: 19392
15. Thrawst
4:07 AM GMT on April 21, 2014
Thank you, Cody.
Member Since: July 18, 2010 Posts: 50 Comments: 1909
14. Astrometeor
3:55 AM GMT on April 21, 2014
3 months and 9 days later, Cody posts a new blog.

Thanks Cody.
Member Since: July 2, 2012 Posts: 101 Comments: 10500
13. TylerStanfield
3:14 AM GMT on April 21, 2014
Quoting 12. TropicalAnalystwx13:


Well, the whole premise of us being in the active era comes from the fact that the AMO turned positive in 1995. It's not positive this year. As far as us being in an era of greater observation due to enhanced technology, I did debate going higher with my numbers. Given the potential for a strong El Nino though, I went lower. We'll see.

True, I didn't use the "active period" for a reasoning to go higher with my numbers.
See 930. on Dr. Master's blog for more.
Member Since: June 2, 2013 Posts: 9 Comments: 1414
12. TropicalAnalystwx13
3:11 AM GMT on April 21, 2014
Quoting 7. TylerStanfield:

Great post Cody!
Still leaning toward 10 Named Storms, 4 Hurricanes, and 1 Major.
We are in the active, and satellite era, you know.
I think we will see a season similar to 1982 or 1997, but with more of the component of activity focused in the subtropics like 1997 and 1991 did.

Well, the whole premise of us being in the active era comes from the fact that the AMO turned positive in 1995. It's not positive this year. As far as us being in an era of greater observation due to enhanced technology, I did debate going higher with my numbers. Given the potential for a strong El Nino though, I went lower. We'll see.
Member Since: July 6, 2010 Posts: 113 Comments: 32863
11. StormTrackerScott
3:10 AM GMT on April 21, 2014
Daniel Swain @Weather_West

New Wly wind burst likely to extend well east of Dateline; may kick #ElNino evolution into high gear

Link
Member Since: February 28, 2013 Posts: 9 Comments: 4768
10. StormTrackerScott
3:07 AM GMT on April 21, 2014
Quoting 9. Bluestorm5:
Another great blog as usual. I can see you climbing up the latter pretty quickly in tropical meteorology. Hopefully I'll get my own 2014 forecast blog up during the month of May when I do not have school.



Which is why I might push it higher than most people in term of number of storms but I haven't made my final decision yet.


8 3 1 are my numbers. First storm might come in May.
Member Since: February 28, 2013 Posts: 9 Comments: 4768
9. Bluestorm5
3:03 AM GMT on April 21, 2014
Another great blog as usual. I can see you climbing up the latter pretty quickly in tropical meteorology. Hopefully I'll get my own 2014 forecast blog up during the month of May when I do not have school.

Quoting 7. TylerStanfield:

Great post Cody!
Still leaning toward 10 Named Storms, 4 Hurricanes, and 1 Major.
We are in the active, and satellite era, you know.
I think we will see a season similar to 1982 or 1997, but with more of the component of activity focused in the subtropics like 1997 and 1991 did.


Which is why I might push it higher than most people in term of number of storms but I haven't made my final decision yet.
Member Since: August 1, 2011 Posts: 28 Comments: 8075
8. StormTrackerScott
3:02 AM GMT on April 21, 2014
Quoting 6. TropicalAnalystwx13:

The idea of above-average SSTs "spilling over" doesn't make much sense to me. The warm water there exists because of westerly trade winds; trade winds can't "spill over" land, and Central America divides the East Pacific from the Atlantic. I think waters in the Caribbean Sea will stay generally above-average regardless.


I think maybe he was referring to tropical moisture spilling over causing potential systems to form. I could be wrong though.
Member Since: February 28, 2013 Posts: 9 Comments: 4768
7. TylerStanfield
3:00 AM GMT on April 21, 2014
Great post Cody!
Still leaning toward 10 Named Storms, 4 Hurricanes, and 1 Major.
We are in the active, and satellite era, you know.
I think we will see a season similar to 1982 or 1997, but with more of the component of activity focused in the subtropics like 1997 and 1991 did.
Member Since: June 2, 2013 Posts: 9 Comments: 1414
6. TropicalAnalystwx13
3:00 AM GMT on April 21, 2014
Quoting 3. GTstormChaserCaleb:

Good job, Cody. The mean sea level pressure map also shows above average pressures in the Indian Ocean. I asked this question earlier, but is it possible that an El Nino becomes so strong that part of the warming off the coast of Ecuador spills over to the Caribbean and MDR and warms the waters in these regions?

The idea of above-average SSTs "spilling over" doesn't make much sense to me. The warm water there exists because of westerly trade winds; trade winds can't "spill over" land, and Central America divides the East Pacific from the Atlantic. I think waters in the Caribbean Sea will stay generally above-average regardless.
Member Since: July 6, 2010 Posts: 113 Comments: 32863
5. GTstormChaserCaleb
2:39 AM GMT on April 21, 2014
Notice you can see the loop current eddy on the CDAS-SFLUX.
Member Since: June 30, 2013 Posts: 12 Comments: 8774
4. StormTrackerScott
2:32 AM GMT on April 21, 2014
Quoting 3. GTstormChaserCaleb:
Good job, Cody. The mean sea level pressure map also shows above average pressures in the Indian Ocean. I asked this question earlier, but is it possible that an El Nino becomes so strong that part of the warming off the coast of Ecuador spills over to parts of the Caribbean and warms the waters there?


I agree, I think we may get some spill over into the Caribbean especially early on and again come September. I remember lost of tropical moisture coming across FL from systems moving NE from the E-Pac then into the Gulf however the treck across Mexico just left tropical moisture which sheared across FL.

Look at Cody's week 4 850 wind vector map and you can kinda see this and this is why the GFS is jumping the gun on Caribbean development. I don't buy that scenario but an abundance of tropical moisture for FL and the Bahamas maybe in the cards come the first week of May.





Member Since: February 28, 2013 Posts: 9 Comments: 4768
3. GTstormChaserCaleb
2:28 AM GMT on April 21, 2014
Good job, Cody. The mean sea level pressure map also shows above average pressures in the Indian Ocean. I asked this question earlier, but is it possible that an El Nino becomes so strong that part of the warming off the coast of Ecuador spills over to the Caribbean and MDR and warms the waters in these regions?
Member Since: June 30, 2013 Posts: 12 Comments: 8774
2. PedleyCA
2:15 AM GMT on April 21, 2014
Sounds good to me....
Member Since: February 29, 2012 Posts: 0 Comments: 6254
1. beell
2:07 AM GMT on April 21, 2014
Nice work, TA. A good read.
Thanks!
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About TropicalAnalystwx13

Teenager. Weather aficionado. Soccer fan. Realist. Posts subject to sarcasm. Goal: National Hurricane Center.

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