# Presentation: 424350

## NOAA’s 2007 Atlantic Hurricane Outlook Date Issued: 9 August 2007 

**       ****Season and                      2007 Outlooks        1951-2000**
**      **_**Activity Type                  August      May          Normals         **_

**Chance Above Normal          85%         75%**
**Chance Near Normal            10%         20%**
**Chance Below Normal            5%           5%                                 **
**Named Storms                     13-16         13-17                11**
**Hurricanes                               7-9           7-10                  6**
**Major Hurricanes                   3-5             3-5                  2**
**ACE Index (% Medn)     140-200     125-210             100**

**Notes:**
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.

## Historical Atlantic Seasonal Activity 

- The 2007 Atlantic hurricane season outlooks reflects the ongoing active Atlantic hurricane era that began in 1995, ongoing warmer Atlantic SSTs, and ENSO-neutral or La Niña conditions.

## Expected August-October 2007 Conditions

**Conditions e****xpected during August-October 2007 ****reflect**** the ongoing active Atlantic hurricane era, ****ongoing warmer Atlantic Ocean temperatures in the west, and**** La Niña-like patterns of tropical convection and wind shear. **

**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. 

## Multi-Decadal Signal in Atmosphere

_**Above-Normal Seasons feature**_**:**
**Reduced  vertical wind shear in boxed region is critical for hurricane formation.**
**Weaker easterly winds in boxed region are associated with northward shift  of  the ITCZ and a more favorable African Easterly Jet (AEJ).**
**Enhanced cyclonic circulation is aligned along equatorward flank of AEJ  (boxed region), and provides energy to developing tropical disturbances.**

## 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**

## 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. Similar conditions were also present during the active period 1950-1970, and opposite anomaly patterns were associated with the below-normal hurricane era 1971-1994. The current convection patterns favor expanded upper-level easterlies (green arrow) and weaker trade winds (blue arrow) across the tropical Atlantic, which contributes to warmer SSTs, reduced vertical wind shear, and a more favorable African easterly Jet.**

**7**

## SST Departures (oC) in the Tropical Pacific Ocean During the Last 4 Weeks

**Recent sea-surface temperatures (SSTs) in the equatorial Pacific Ocean were more than 1****oC below average in between ****130oW ****and the South American coast, and more than 0.5****o****C above average in portions of the western Pacific. This pattern reflects the continued evolution toward a La Niña episode.**

## Recent Pattern of Anomalous Tropical Convection

**The pattern of tropical convection (indicated by anomalous Outgoing Longwave Radiation) continues to be La Niña-like, with suppressed convection across the central and east-central equatorial Pacific (orange shading), and **
**enhanced convection over the western equatorial Pacific (blue shading).**

## Atlantic Sea-Surface Temperature Departures (oC) During June-July 2007

**Sea-surface temperatures remain above average across the western tropical Atlantic and Caribbean Sea (Red box). Departures during June-July 2007 were the fifth warmest since 1950 (averaging 0.56****o****C). **
**Sea-surface temperatures in the eastern tropical Atlantic (Blue box) dropped to only slightly above-average (0.17****o****C) levels during June-July, but have now begun warming back up. **