# Presentation: 693468

## NOAA 2008 Atlantic Hurricane Season Outlooks

**NOAA 2008 Atlantic Hurricane Season Outlooks**

**                                               ****2008 Outlooks**
**                                           ****August       May 22**
**      **_**Activity Type              Update                             Normals         **_

**Chance Above Normal        85%               65%**
**Chance Near Normal           10%               25%**
**Chance Below Normal           5%               10%**
**                                                 **
**There is increased confidence (85% chance) the 2008 season will be above normal. In May, we emphasized “normal to above-normal, with an above-normal season most likely.”**
**Tropical Storms                  14-18                12-16                    11**
**Hurricanes                            7-10                   6-9                        6**
**Major Hurricanes                 3-6                     2-5                       2**
**ACE (% Median)            140%-230%   100%-210%           100%**

**Based on past seasons with similar climate conditions and similar early season activity, the August outlook indicates a 67% probability for each range. These ranges are all in the “above-normal” category.**

**Notes:**
The OutlookFor 2007, we are predicting a very high probability (***%) of an above-normal Atlantic Hurricane Season, and there is a strong possibility the season could be extremely active.  

We are forecasting: XX to XX named storms, with XX to XX becoming hurricanes, of which XX to XX could become major hurricanes of Category 3 strength or higher. 

Although NOAA does not make an official hurricane landfall forecast, historically, seasons with similar levels of activity have averaged 2-4 U.S. landfalling hurricanes, and 2-3 hurricanes in the region around the Caribbean Sea.
 However, it is currently not possible to confidently predict at these extended ranges the exact number or intensity of landfalling hurricanes, or whether or not a given locality will be impacted by a hurricane this season.

## Expected August-October 2008 Conditions

**The above conditions are now in place as predicted in May, and have already been associated with ****strong early-season activity over the tropical Atlantic and Caribbean Sea.**
**These conditions reflect**** the ongoing active Atlantic hurricane era,**** warmer Atlantic SSTs, ****and a lingering La Niña influence.**

**Notes:**
The science behind the outlookThe climate patterns expected to produce the above-normal 2007 season are the ongoing multi decadal signal, warmer Atlantic Ocean temperatures, and the possible development of a La Niña episode in the tropical Pacific Ocean. 
The multi-decadal signal reflects the overall set of conditions responsible for the very active hurricane seasons since the current active era began in 1995.  Since 1995, 9 of the last 12 hurricane seasons have been above normal, and the rate of hurricane landfalls has increased sharply. 

## Likely Activity for Remainder of 2008 SeasonAugust 7th through -November 30th

**9-13 Named Storms**
**5-8 Hurricanes**
**2-5 Major Hurricanes (Cat. 3-5 on Saffir-Simpson Scale)**

**5 Tropical Storms **
**2 Hurricanes**
**1 Major Hurricane (Bertha); longest July storm on record**
**ACE index = 46% of median---Third highest on record**

**2008 Activity to Date**

## Historical Atlantic Seasonal Activity 

**NOAA’s updated 2008 Atlantic hurricane season outlook indicates ****a likely (67% chance) ACE range of 140%-230% of the median****. This is well within the “above-normal” category.**

## SST Departures (oC) in the Tropical Atlantic Ocean

**July SST departures averaged +0.33****o****C, consistent with an above-normal season.**

**SST Departures (****o****C) in the Tropical Atlantic Ocean**

## Lingering La Niña Influence

**La Niña has dissipated as indicated by a warming of the sea-surface temperature (SST) departures across the central and east-central equatorial Pacific between early April (Left) and July (Right). **
**However, a horse-shoe shaped pattern of SST departures linked in part to La Niña still persists. This pattern suggests the lingering La Niña-related pattern of tropical convection will continue, and that ENSO will not hinder Atlantic hurricane activity.**

**Lingering La Niña Influence**
**4-Week SST Departures (****o****C) in the Tropical Pacific Ocean**

## Lingering La Niña influenceAnomalous Equatorial Convection and Winds

**Lingering La Niña influence****Anomalous Equatorial Convection and Winds**

**Lingering La Niña impacts near the date line include suppressed convection (orange/red- Left panel) and weaker tropical easterly winds (blue-Right panel).**

**OLR Anomalies**

**850-hpa Zonal Wind Anomalies**

**Longitude**

- (August-November)** **

**Longitude**

## Explained variance = 82%.

**The transition into the current active Atlantic hurricane era is captured by a phase change in tropical multi-decadal signal (Bell and Chelliah, J. Climate, 15 Feb. 2006).**

**Explained variance = 82%.**

**Observed**** ****vs.**** Multi-Decadal Signal**

**Transition to Current Active Atlantic hurricane era **

## Underlying Climate Pattern forActive Atlantic Hurricane Era

**Drier**

**Warmer**

**Warmer**

**Wetter**

**The combination of an enhanced West African monsoon system and suppressed convection over the Amazon Basin has been in place since 1995. This pattern favors expanded upper-level easterlies (green arrow) and weaker trade winds (blue arrow), which contribute to warmer SSTs, reduced vertical wind shear, and a more favorable African easterly Jet.**

## Mean Divergent Anomalies at 200-hPa

**The current upper-level divergent pattern (Top) is consistent with the ongoing active hurricane era (Bottom). Key features include an enhanced West African monsoon system and anomalous convergence over the eastern Amazon Basin.**

**1995-2005 **

## Mean Circulation Anomalies at 35,000 Feet

**Current upper-level circulation anomalies (Top) indicate an enhanced subtropical ridge in both hemispheres across Africa and the Atlantic Ocean (red shading in NH, blue shading in SH). These patterns are also consistent with the ongoing active hurricane era (Bottom).**

**1995-2005 **

## 700-hpa Circulation Anomalies

**The active hurricane era also features westerly anomalies (solid lines, Top), indicating weaker tropical easterlies, extending from the eastern Pacific to Africa. **
**This pattern is associated with increased cyclonic shear (red shading) across the main development region (green box). These patterns are now in place (Bottom).**
** ****These anomalies produce an exceptionally favorable African Easterly Jet, and significant development of African easterly waves in the main development region.**