# Presentation: 673527

## On NOAA’s Hurricane outlooks Muthuvel ChelliahClimate Prediction Center/NCEP

**NOAA's 33rd Climate Diagnostics and Prediction Workshop/CLIVAR Drought Workshop (CDPW), October 20-24, 2008 in Lincoln, Nebraska**

## NOAA has been issuing Long lead Hurricane outlooks for about a decade now.

The basis of these outlooks, lessons learned and some preliminary thoughts on science versus public expectations.

- The basis of these outlooks, lessons learned and some preliminary thoughts on science versus public expectations.

## Hurricane seasons, in different ocean basins around the world, are “regular” seasonal/annual feature.

It happens every year, just like, say Summer/Winter Monsoon over Asia.

But how do the variability of the “basic  characteristics” of these seasonal features compare?

Let’s very briefly compare the North Atlantic Hurricane season and the Indian summer monsoon. 

- It happens every year, just like, say Summer/Winter Monsoon over Asia.
- But how do the variability of the “basic  characteristics” of these seasonal features compare?
- Let’s very briefly compare the North Atlantic Hurricane season and the Indian summer monsoon.

## All-India Summer Monsoon (June-September) Rainfall (AISMR) 

**All-India Summer Monsoon (June-September) Rainfall (AISMR) **
**Anomalies during 1871-2003**

- Source: Monsoon On Line

- One of the worst summer monsoon failures and droughts in India in the past century. It is also the start of the famous “most severe Sahel drought in N.Africa”

**  ****Asian monsoon: REGULAR annual feature. **
**  ****Will definitely happen every year.**
-  **Long-term Mean  =   ****853  mm**
**  **_**Standard Deviation**_** = 85 mm (about 10% of Mean)**
**  **_**Normal season**_**:  ****within 10%**** of Mean**
**  **_**Range**_** ****~ 70% - 120%****  of  Mean**

## 1951-2000 ACE: 

- Mean:	93
**Std:** 54 (58% of Mean)
- Range: 17-227

_**ACE:**_ Accumulated Cyclone Energy (Bell et al. 2000) [similar to Bill Gray’s** **earlier** **_**HDP**_: Hurricane Destructive Potential. ] - It is an _accumulated sum of squared max. sustained wind speed_ every 6hours for all named storms (and hurricanes) for the whole season.

## Transition to generally MORE INACTIVE seasons. (exactly when ? ‘68? ‘70? ‘72? Late 60’s? Early 70s?) 

- _MORE ACTIVE_ seasons? May be, Yes!

- Transition to generally _MORE_ _INACTIVE_ seasons. (exactly when ? ‘68? ‘70? ‘72? Late 60’s? Early 70s?)

- Sharp transition in 1995 to  _MORE ACTIVE_  seasons

- The atmospheric conditions associated with, or attributable to, this transition were better understood and discussed (Chelliah &Bell, 2004; Bell & Chelliah, 2006)

**The reasons for this ‘sudden’ transition are less clear. But IT happened, and **_**we have been in an ‘active phase’ since 1995 (but until when ?).**_**  **_**This very fact is very much THE basis our NOAA’s hurricane outlooks.**__** **_

-    2.2
-    1.1
-    0.9
-    0.7
-   -0.8

## NOAA’s Official Hurricane Outlooks (Probability Forecasts)

**NOAA’s Official Hurricane Outlooks (Probability Forecasts)**

**Year/Season        A     N     B          ****OBS****         A     N     B**
-     1999                 A                           **A **            A
-     2000                _**75**_    50   25	          A	         _**40**_   _**40**_    20
-     2001                35    _**45**_   20           N             10   _**50**_    40
-     2002                35    _**45**_   20           B             10   _**50**_    40
-     2003                _**55**_    35   10   **P**      **A**             _**60**_   35      5
-     2004                _**50**_    40   10           **A**             _**45**_   _**45**_    10
-     2005                _**70**_    20   10   **P**      **A**        _**95-100**_
-     2006                _**80**_    15     5           N             _**70**_   20      5
-     2007                _**75**_    20     5           N             _**85**_   10      5
-     2008                _**65**_    25   10   **P** 	         _**85 **_  10      5

_**MAY Outlook**_	        _**AUG Outlook**_

**CPC’s ONI (Oceanic Nino Index)**

| 1995 | -0.5 |
| --- | --- |
| 1996 | -0.1 |
| 1997 | 2.2 |
| 1998 | -1.1 |
| 1999 | -1.0 |
| 2000 | -0.4 |
| 2001 | 0.0 |
| 2002 | 1.1 |
| 2003 | 0.5 |
| 2004 | 0.9 |
| 2005 | 0.2 |
| 2006 | 0.7 |
| 2007 | -0.8 |
| 2008 | N |

## August 2006:  Expected Activity - 75% chance above normal, 20% chance near normal, 5% chance below normal.  .. Multi-decadal fluctuations in Atlantic hurricane activity Atlantic hurricane seasons exhibit prolonged periods lasting several decades of generally above-normal or below-normal activity. ... ENSO is not expected to impact this hurricane season ( so, activity will be high)

_**August 2007:**_** Expected Activity -** **85% chance above normal, 10% chance near normal, 5% chance below normal** Expected Climate Conditions – **Active multi-decadal signal, La Niña-like pattern of tropical convection, warmer western tropical Atlantic and Caribbean Sea: **The prediction for an above-normal 2007 hurricane season reflects the combination of two main climate factors: 1) _the continuation of conditions that have been conducive to above –normal conditions since 1995_ and 2) the continued La Niña-like pattern of tropical convection. All features of the multi-decadal signal are already in place across the tropical Atlantic, as is a persistent La Niña-like pattern of tropical convection across the eastern half of the equatorial Pacific. (_**__* so, activity will be high*_)
_**August 2008:**_**  Expected Activity -** **85% chance above normal, 10% chance near normal, 5% chance below normal** Expected Climate Conditions – 1) The multi-decadal signal, which has been conducive to above-normal Atlantic hurricane activity since 1995, and which includes above-normal Atlantic sea-surface temperatures, and 2) a lingering La Niña signal as reflected in Pacific Ocean temperatures, convection and winds (_**__* so, activity will be high*_)
*** **so, activity will be high* for every year may be appropriate for a “decadal type outlook”, but not for seasonal outlook, especially when the ‘causal factors’ _and the influence of ENSO in a changing climate are not well known_.

## NOAA’s Atlantic hurricane season classifications -Official

_***Above-normal season***__**:**_ 1) _An ACE index value well above 103 x 10__4 __kt2_ (corresponding to _117% of the median_ ACE value or 110% of the mean), **OR** 2) _an ACE value slightly above 103 x 104 kt2_ _**combined with at least two of the following three parameters being above**__ the long-term average:_ number of named storms, hurricanes, and major hurricanes.
_***Near-normal season***__**:**_ _An ACE index value in the range_ 66-103 x 104 kt2 (corresponding to _75%-117% of the median_ or 71%-110% of the mean), **OR** an ACE index value _slightly above_ 103 x 104 kt2 **but **_**with less than two of the following three parameters being above the long-term average:**_ numbers of named storms, hurricanes, and major hurricanes.
_***Below-normal season***__**:**_ _An ACE index value_ below 66 x 104 kt2, corresponding to _below 75% of the median_ or 71% of the mean.
- -------Definitions of Above/Normal/Below are complex, it should be more simple and objective, say based on std. alone of ACE.  The results are not too different, if at all they are only slight that too only in “normal”

|  | # of TS | Range of TS | # of H | Range of H | # of MH | Range of MH |
| --- | --- | --- | --- | --- | --- | --- |
| Above-Normal | 13.7 | 10-28 | 8.6 | 6-15 | 2.8 | 2-8 |
| Near-Normal | 9.4 | 6-14 | 5.6 | 4-8 | 1.9 | 1-3 |
| Below-Normal | 6.9 | 4-9 | 3.7 | 2-5 | 1.1 | 0-2 |
| All Seasons | 10.3 | 4-28 | 6.2 | 2-15 | 2.7 | 0-8 |

***NOAA uses :   1) ACE index,    ***_***combined with***_***    ***
***                         ******2)  the #s of named storms (NS), hurricanes (H), & major hurricanes (MH) ***
***to categorize hurricane seasons as being  Above-Normal,  Near-Normal, or  Below-Normal.***

## In closing ....

- NOAA outlooks – from a public perspective may be ok. CPC is doing a good job.
- 		- Imagine if we had predicted a ‘normal or below normal season this year (2008) with all the landfalls and so on (which we do not predict anyway),
- 		- even though the media criticized the outlooks last couple of years at the end of the season, as the totals came in,  but the public/media attention of scrutiny was not high during the season, due to lack of many landfalling systems.
- So as we move to the second decade of NOAA hurricane outlooks, we have to not only worry about media, but also the science behind the outlooks, the scientific scrutiny,
- 		-Objective classification of seasons
- 		-Objective forecast methods (reproducible results, etc.)
- 		-More optimal use of high resolution GCM based guidance/outlooks 	for actual systems (TS/H/MH) and of course the ACE itself _with _	_proper bias corrections_**,** which the Europeans have already begun to 	do and 	implement.  The ensemble runs should give a good idea of 	the uncertainties in the outlook and hence a more objective 	probabilities based hurricane outlook.

## ACE forecast by Objective methods using CFS hindcasts for the Entire season (from Hui Wang)

| Mthd 3 | IC04 |  |  | IC07 | OBS |
| --- | --- | --- | --- | --- | --- |
| 2002 | 70 |  |  | 58 | 66 |
| 2003 | 172 |  |  | 125 | 175 |
| 2004 | 166 |  |  | 133 | 225 |
| 2005 | 197 |  |  | 212 | 248 |
| 2006 | 182 |  |  | 156 | 79 |
| 2007 | 248 |  |  | 176 | 68 |
| 2008 | 177 |  |  |  |  |
| RMSE | 91 |  |  | 70 |  |

**ACE forecast by Objective methods using CFS hindcasts for the Entire season (from Hui Wang)**

| Mthd 2 | IC04 |  |  | IC07 | OBS |
| --- | --- | --- | --- | --- | --- |
| 2002 | 98 |  |  | 72 | 66 |
| 2003 | 159 |  |  | 127 | 175 |
| 2004 | 157 |  |  | 134 | 225 |
| 2005 | 180 |  |  | 205 | 248 |
| 2006 | 174 |  |  | 156 | 79 |
| 2007 | 216 |  |  | 173 | 68 |
| 2008 | 172 |  |  |  |  |
| RMSE | 83 |  |  | 70 |  |

-  Root mean square error of ACE, in these forecasts ( whether it is from April (IC04) initial conditions or August (IC07) conditions)  is higher than the total ACE itself in some years., suggesting probability outlook is of course the way to go thus clearly expressing the possible uncertainties.

## Slide 12

## Slide 13

## CPC’s Oceanic Nino Index by season

| 2000 |  |  |  |  |  | -0.6 | -0.4 | -0.4 | -0.4 | -0.5 |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 2001 |  |  |  |  |  | 0.1 | 0.1 | 0.0 | 0.0 | -0.1 |  |  |
| 2002 |  |  |  |  |  | 0.8 | 0.9 | 0.9 | 1.1 | 1.3 |  |  |
| 2003 |  |  |  |  |  | 0.0 | 0.3 | 0.4 | 0.5 | 0.5 |  |  |
| 2004 |  |  |  |  |  | 0.4 | 0.7 | 0.8 | 0.9 | 0.8 |  |  |
| 2005 |  |  |  |  |  | 0.5 | 0.5 | 0.3 | 0.2 | -0.1 |  |  |
| 2006 |  |  |  |  |  | 0.3 | 0.4 | 0.5 | 0.7 | 0.9 |  |  |
| 2007 |  |  |  |  |  | -0.1 | -0.2 | -0.5 | -0.8 | -1.1 |  |  |
| 2008 |  |  |  |  |  | -0.4 | -0.1 | 0.0 |   |   |  |  |

| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |

- _[  ](http://weather.unisys.com/hurricane/atlantic/2002H/track.gif)_
**Individual Storm Summary**
- Winds in knots, pressure in millibars, category is based on Saffir-Simpson scale.

| 
# | Name | Date | Wind | Pres | Cat |   |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | Tropical Storm ARTHUR  | 14-16 JUL  | 50  | 997  | - |   |
| 2 | Tropical Storm BERTHA  | 04-09 AUG  | 35  | 1008  | - |   |
| 3 | Tropical Storm CRISTOBAL  | 05-08 AUG  | 40  | 999  | - |   |
| 4 | Tropical Storm DOLLY  | 29 AUG-04 SEP  | 55  | 994  | - |   |
| 5 | Tropical Storm EDOUARD  | 01-06 SEP  | 55  | 1002  | - |   |
| 6 | Tropical Storm FAY  | 05-08 SEP  | 50  | 998  | - |   |
| 7 | Tropical Depression SEVEN  | 07-08 SEP  | 30  | 1009  | - |   |
| 8 | Hurricane GUSTAV  | 08-12 SEP  | 80  | 960  | 1 |   |
| 9 | Tropical Storm HANNA  | 12-14 SEP  | 45  | 1001  | - |   |
| 10 | Hurricane ISIDORE  | 14-26 SEP  | 110  | 934  | 3 |   |
| 11 | Tropical Storm JOSEPHINE  | 17-19 SEP  | 50  | 1004  | - |   |
| 12 | Hurricane KYLE  | 20 SEP-12 OCT  | 75  | 980  | 1 |   |
| 13 | Hurricane LILI  | 21 SEP-04 OCT  | 125  | 938  | 4 |   |
| 14 | Tropical Depression FOURTE | 14-16 OCT  | 30  | 1002  | - |   |