2011 Atlantic Hurricane Season Forecast

By: MiamiHurricanes09 , 2:12 AM GMT on May 26, 2011

ENSO (El Niño-Southern Oscillation)
• The Basics •

• Quasi-periodic climate pattern.

• Occurs over equatorial Pacific.

• Characterized under two stages: El Niño (when the anomalous sea surface temperature across the equatorial Pacific is above 0.5˚C) and La Niña (characterized when the anomalous sea surface temperature across the equatorial Pacific is below -0.5˚C).

• Should the anomalous sea surface temperature be between the aforementioned temperatures, then it can be characterized as neutral conditions, however, these conditions do not last as long as an El Niño or La Niña phase.

• Southern Oscillation Index (SOI) is defined as the air pressure difference between Tahiti and Darwin.

• When the SOI is in its positive phase, higher air pressure dominates over Tahiti and Darwin, producing for trade winds along the equatorial Pacific to increase. When this occurs, upwelling of water takes place, bringing cooler water from below the surface upwards. This is a key ingredient in the development of La Niña conditions across the equatorial Pacific.

• The opposite would be when the SOI is in its negative phase. When this occurs, the air pressure over Darwin is greater as opposed to Tahiti, and so, trade winds over the equatorial Pacific are weaker, thus constituting for lesser amounts of upwelling, and thus allowing for sea surface temperatures to increase or remain steady. When the SOI is in its negative phase, we are seeing an increase in trade winds over the Atlantic basin, which then constitutes for an increase in vertical wind shear (a factor of an El Niño season).

ENSO (El Niño-Southern Oscillation)
• The Forecast •

• The ENSO consists of 4 regions: Niño 1+2, Niño 3, Niño 3.4, and the Niño 4. The Niño 3.4 plays the largest role in the atmospheric conditions across the Atlantic, and so this will be the region discussed below.

• Following the center-line on the graph to the right, dynamical forecast models foresee that sea surface temperature anomalies remain neutral for the 2011 Atlantic Hurricane Season. However, forecasts change on a month-to-month basis and what we see here by no means is set in stone.

• Should this forecast verify to some extent, one major impact that we will see in the Atlantic is the reduction of upper-level winds to an average or slightly below average mean for the upcoming season.

Sea Surface Temperatures
• The Basics •

• One of the many key ingredients in the development of tropical cyclones are warm sea surface temperatures.

• Tropical cyclones feed off of latent heat from warm waters as water vapor rises into the cyclones’ circulation. This then allows for the cyclone to continue to strengthen and grow more powerful should surrounding conditions be conducive.

• Sea surface temperatures also play a large role in the Madden-Julian Oscillation (MJO), which will be discussed later.

Sea Surface Temperatures
• The Forecast •

• Models currently foresee sea surface temperatures across the Atlantic to continue to warm. Although we are currently below the levels of warmth we achieved in hyperactive seasons such as 2010 and 2005, we are very close to 2008’s levels.

• It should be noted that if sea surface temperatures were to warm excessively across the north Atlantic, we run the risk of losing the north Atlantic tri-pole which plays a large role in the location of the MJO during the season.

Madden-Julian Oscillation (MJO)
• The Basics •

• The Madden-Julian Oscillation (MJO) is an easterly propagating wave of enhanced rainfall that dwells over the warm(est) parts of tropical oceans across the Earth.

• The upward motion of the MJO, or increased anomalous rainfall, tends to spend more time over warmer waters, as opposed to cooler waters, which is where the downward motion, or suppressed anomalous rainfall tends to dwell over.

• For example, 2010 had upward motion of the MJO focused mainly over the Atlantic ocean (hence one of the reasons we saw so much tropical activity). But at the same time, the downward motion was providing for suppressed rainfall over the Pacific, because that’s where the cool waters of the La Niña were dwelling, causing for them to have one of the most inactive seasons to date.

Madden-Julian Oscillation (MJO)
• The Forecast •

• 2011 is likely to have upward motion of the MJO dwell over the Atlantic for increased periods of time due to the fact that sea surface temperatures are forecast to increase to above-average levels.

• Additionally, we will have the cold signature of the PDO, the north Atlantic tri-pole, and possibly slightly below-average sea surface temperatures over the equatorial Pacific all in tandem focusing heat, and thus the upward motion of the MJO, into the Atlantic.

North Atlantic Oscillation (NAO)
• The Basics •

• The North Atlantic Oscillation (NAO) is characterized as the pressure difference between the Icelandic Low and the Azores High.

• When the NAO is in its negative phase the subtropical ridge weakens, and thus allows for trade winds to slacken and cause less upwelling which in turn allows for sea surface temperatures to increase. When the NAO is positive, the subtropical ridge strengthens and causes for stronger trade winds and more upwelling of cooler waters from below the surface.

• The NAO is also a main factor in the steering of tropical cyclones. When the NAO is in its negative phase, yes the subtropical ridge is weaker, but do to this troughiness along the eastern seaboard is also weaker, which then reduces the chance of a recurving cyclone, and increases the chances of a landfall along a major landmass.

North Atlantic Oscillation (NAO)
• The Forecast •

• Models forecast that the subtropical ridge stay relatively weak for the most part, during this upcoming season, indicating a negative NAO.

• Should this verify, we should see continued increase in sea surface temperatures, less SAL, and an increased chance for a landfall along a major landmass.

• As mentioned previously, when the NAO is positive, trade winds increase. In the process of this occurring, these winds blow dry air (SAL -- Saharan Air Layer) into the mid to upper levels of the atmosphere from the Sahel. When this occurs, African easterly waves (AEW’s) have a difficult time developing due to the fact that they are being choked by dry air, and are unable to develop consistent thunderstorm activity. This is the opposite of what is currently being forecasted.

Mean Sea Level Pressure (MSLP)
• The Basics •

• Low pressure favors condensation, upward motion, instability, etc, which is conducive for the development of tropical cyclones.

• High pressure favors sinking air and fair conditions, which is not conducive for the development of tropical cyclones.

Mean Sea Level Pressure (MSLP)
• The Forecast •

• The ECMWF forecasts that MSLP be at below average levels for the majority of the Atlantic for the months of June through August, with MSLP being at very low levels across the Gulf of Mexico.

• This same trend continues for the months of August through October, with the exception of a tad bit higher pressures than the aforementioned months be present over most of the western Atlantic.

• Note the slightly lower pressures over the subtropical Atlantic during the latter months, signifying a weaker subtropical ridge and most likely a negative NAO.

• The Forecast •

• The ECMWF forecasts that above average levels of precipitation be present over the Caribbean and extreme southwestern Atlantic for the months of June through August.

• Higher amounts of precipitation move more towards the eastern Atlantic and Caribbean for the months of August through October.

• Final Result •

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5. AtHomeInTX
11:48 PM GMT on May 26, 2011
Wow! Great job MH9! Detailed AND understandable. I especially liked the NAO explanation. :) Looks to be a busy season.
Member Since: August 24, 2010 Posts: 0 Comments: 549
4. KoritheMan
2:51 AM GMT on May 26, 2011
Nice blog. I'm still going with 15/8/4, myself.
Member Since: March 7, 2007 Posts: 617 Comments: 22390
3. MiamiHurricanes09
2:38 AM GMT on May 26, 2011
Quoting GainesvilleGator:
I didn't hear any audio on your video. Nice blog.
Yup, I made it intentionally that way because it was made in Keynote (Mac's answer to PowerPoint). Sorry about the poor quality as well, iMovie decided to not open this evening, so 480p is that best we have.
Member Since: September 2, 2009 Posts: 130 Comments: 21388
2. GainesvilleGator
2:33 AM GMT on May 26, 2011
I didn't hear any audio on your video. Nice blog.
Member Since: September 11, 2005 Posts: 4 Comments: 750
1. TropicalAnalystwx13
2:20 AM GMT on May 26, 2011
I agree with your hurricane season predictions. Good post!
Member Since: July 6, 2010 Posts: 128 Comments: 35287

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