# Presentation: 349350

## NOAA’s seasonal forecasts:  A retrospective look at the exceptional 2005 season and a look ahead to 2006

- Eric Blake, Richard Pasch,
- Chris Landsea (TPC)
- Gerry Bell, Muthuvel Chelliah (CPC)
- Stan Goldenberg (HRD)

**Notes:**
Seasonal forecast is a joint effort between CPC/HRD and TPC.

## Outline

- Methodology for seasonal forecast
- Conditions in 2005
- Verification
- (Very) Tentative outlook for ‘06

## NOAA Forecast Methodology

- Assess states of the on-going multi-decadal signal, ENSO, and Atlantic SSTs.
- Use available CPC/CDC forecasts for ENSO/Atlantic SSTs, incorporate any analog techniques and assume persistence of upper-level conditions.
- Predict range of overall activity and probabilities of above-, near-, and below-normal seasons.
- Qualitative/Quantitative process.

**Notes:**
What goes into the forecast?  Every one of the members brings a different element... CPC has the ENSO forecast, TPC generally monitors what has been going on etc.  Mix of qualitative/quantitative ideas... whether it be a nino forecast

## A good measure of seasonal hurricane activity: “Accumulated Cyclone Energy”, or “ACE”

- ACE is defined as the sum of the squares of the wind speed every six hours for all tropical and subtropical storms and hurricanes.
- Therefore, ACE is maximized for long-lived, intense hurricanes, such as Ivan (2004).

**Notes:**
Similar to Gray’s Net Tropical Cyclone parameter (NTC).  

## NOAA’s ACE index expressed as percent of the 1951-2000 median value.  Definitions of season types are indicated by the background shading, with pink, yellow, and blue indicating above-, near-, and below-normal seasons, respectively.

## Tradewinds 50-70% of average during preceding winter/spring 

- Tradewinds 50-70% of average during preceding winter/spring

## Weakened tradewinds likely the main cause of record warmth in the deep tropical Atlantic Ocean before hurricane season

- Leftover El Niño

## NOAA’s 2005 Atlantic Hurricane Outlook               Issued 16 May 2005

**     **_**Activity Type               Outlook          Observed              Mean**__**         **_

**Chance Above Normal        70%      ****Above Normal****	****	****33%**
**Chance Near Normal           20%****	****	****	****	****33%**
**Chance Below Normal         10 %****	****	****	****	****33%**
**                                                 **
**Tropical Storms                   12-15                 27 *********                      11**
**Hurricanes                              7-9                   15*********                        6**
**Major Hurricanes                  3-5                    7                          2**
**ACE % of Median            120%-190%       285%*********               ~100%**

**NOAA’s 2005 Atlantic Hurricane Outlook****               Issued 16 May 2005**

- ***All-time record**

**Notes:**
For last year, NOAA was contemplating no El Nino... a year after a very active 2003... and a warm tropical Atlantic (but cooling slightly).  We put the highest probability in the above normal category and thought there was only a marginal chance of a quiet year.  

## Lowest early season pressure anomalies ever

## Extremely low early season shear

## Warmest Sea-Surface Temperature Anomalies Ever

## NOAA’s 2005 Atlantic Hurricane Outlook Issued 2 Aug 2005

**       ****Season and                    2005                2005           Climatological **
**     **_**Activity Type               Outlook          Observed              Mean**__**         **_

**Chance Above Normal        95%      ****Above Normal****	****	****33%**
**Chance Near Normal           5%****	****	****	****	****33%**
**Chance Below Normal         0 %****	****	****	****	****33%**
**                                                 **
**Tropical Storms                   18-21                  27                      11**
**Hurricanes                              9-11                  15                 ****	****6**
**Major Hurricanes                  5-7                     7               ****	****2**
**ACE % of Median           180%-270%        285%                 ~100%**

**Notes:**
Best to slightly reduce the chance of above normal and lower the top end of the ACE range just a tad.  Turned out to be the wrong move.

## LOW-LEVEL CIRCULATION ANOMALIES FAVORED DEVELOPMENT/INTENSIFICATION       IN THE WESTERN PART OF THE BASIN (?)

**LOW-LEVEL CIRCULATION ANOMALIES FAVORED DEVELOPMENT/INTENSIFICATION       IN THE WESTERN PART OF THE BASIN (?)**

## Slide 14

**Notes:**
50-60% of the time within fcst range

## Slide 16

**Notes:**
75% within the range.  

## 2006 Forecast?

**2006 Forecast?**
- Atlantic SSTs are a little warmer than average.

-  Early March 2005

-  Early March 2006

- But nowhere near as warm as last year!

##           Climate Forecast System (CFS)

Coupled global model (T62L64)
Integrate for 10 months with 60 ensemble members
Objective predictions of 200 mb streamfunction, vertical wind shear and SSTs.
Shown to have skill comparable with statistical models in Nino 3.4 SST hindcasts
Hints of skill in forecasting year-to-year changes in important parameters that control hurricane variability

- Coupled global model (T62L64)
- Integrate for 10 months with 60 ensemble members
- Objective predictions of 200 mb streamfunction, vertical wind shear and SSTs.
- Shown to have skill comparable with statistical models in Nino 3.4 SST hindcasts
- Hints of skill in forecasting year-to-year changes in important parameters that control hurricane variability

**Notes:**
Moving on to new things in the forecast.... The CFS could really assist making forecasts of upper-level conditions... SST... shear.... All parameters that with a three month lead time.  If we were really dreaming there might even be a mean 500 map for the season which could lead to areas of higher and lower risk for landfalls. 

## CFS Seasonal Forecasts of SST from Mar 17

**Notes:**
Forecasts for ASO this year... generally a neutral pattern in the pac and warm in the atlc in the red box.  However there isn’t much skill at this time frame but we should have a better idea in late April.  Last year the CFS too quickly cooled the Atlc waters but was very good in the EPAC.

## Latest Nino 3.4 SST guidance

**Notes:**
Model forecasts are for a generally decrease or hold steady in the 0.5 range.  This is the toughest time of the year as el nino generally decides what it is going to do in the spring

## ENSO neutral conditions forecast by the CFS

- Blah

**ENSO neutral conditions forecast by the CFS**

**Notes:**
The CFS... which has hindcast skill comparable to ENSO CLIPER and other statistical enso forecasts.. Suggests a return to enso neutral... with a rather large spread in ensemble members though by aug!

## February 2006 SST anomalies

- °C

**Notes:**
Here is the last month’s SSTS... warm TATL and a cooling pac tongue.  If you look at how feb SSTs best correlate with ace in the next year...

## Correlations of Feb SSTs to next season’s ACE 

- Correlations of Feb SSTs to next season’s ACE

**Notes:**
Generally the area near Spain is warm... this year it is not... generally the epac is in pattern resembling a cool PDO with cool SSTS s of Alaska.. This year is also not.   A lot of questions that hopefully will be answered as we approach the season... but without a strong el nino with the atlantic very warm... most things point toward an active year.  

## Summary

- 2005 forecasts were too low; verifying numbers were at all-time record levels.
- Early season indications strongly supported NOAA’s  August near-record forecast.
- 2006 hurricane season – preliminary indications are for above normal activity, but probably not  at the levels seen in 2005 (or 2004?)
- Long-wave steering pattern in 2006?

## Slide 25

## H

**H**