Dynamical forecasts of Dynamical forecasts of atmospheric conditions atmospheric conditions

associated with associated with North Atlantic Hurricane Activity by theNorth Atlantic Hurricane Activity by the

Climate Forecast System (CFS) at NCEPClimate Forecast System (CFS) at NCEP

Muthuvel ChelliahMuthuvel Chelliah

Climate Prediction Center/NCEP/NWSClimate Prediction Center/NCEP/NWS

Suranjana SahaSuranjana Saha

Environmental Modeling Center/NCEP/NWSEnvironmental Modeling Center/NCEP/NWS

NCEP’s new Coupled Ocean-Atmosphere NCEP’s new Coupled Ocean-Atmosphere Climate Forecast System (CFS) Climate Forecast System (CFS)

Hindcast Runs Data BaseHindcast Runs Data Base

• Became Operational on 24 August 2004Became Operational on 24 August 2004

• Starts with a set of Atmosphere-Ocean Initial Conditions and Starts with a set of Atmosphere-Ocean Initial Conditions and medium/extended integrations proceed for about 9+ months with medium/extended integrations proceed for about 9+ months with no interference.no interference.

• An extensive data base of hindcast runs (Forecast) from 1981 An extensive data base of hindcast runs (Forecast) from 1981 have been created by the Environmental Modeling Center (EMC).have been created by the Environmental Modeling Center (EMC).

• This study will examine how the CFS and the Hindcast data This study will examine how the CFS and the Hindcast data base can be used to help make NOAA’s North Atlantic Hurricane base can be used to help make NOAA’s North Atlantic Hurricane Outlooks issued every yearOutlooks issued every year

CFC’s Hindcast RunsCFC’s Hindcast Runs1981-2003 1981-2003

Aug-Sep-Oct Peak of the N.Atlantic Hurricane

Season

0 Month Lead (JUL/AUG)

Initial Conditions from

Jul 9, 10, 11, 12, 13

Jul 19, 20, 21, 22, 23

-2, -1, 1, 2, 3 Aug

1-Month Lead (JUN/JUL)

4-Month Lead (MAR/APR)

1981-2003 Aug-Sep-Oct (ASO) mean forecasts made from 4-months (Mar/Apr) to 0-month (Jul/Aug) lead are considered in this study. For each lead there are a total of 15 ensemble member forecasts. Only Ensemble mean forecasts are studied here.

Some background on Some background on

NOAA’s Hurricane OutlooksNOAA’s Hurricane Outlooks

See poster: See poster: The 2004 North Atlantic and East Pacific The 2004 North Atlantic and East Pacific Hurricane Season Summary and NOAA OutlooksHurricane Season Summary and NOAA Outlooks

Muthuvel Chelliah, Gerry Bell and Kingtse MoMuthuvel Chelliah, Gerry Bell and Kingtse Mo

Seasonal North Atlantic ActivitySeasonal North Atlantic ActivityNOAA’s Accumulated Cyclone Energy (ACE) IndexNOAA’s Accumulated Cyclone Energy (ACE) Index

CFS Hindcasts Starts in 1981

NOAA Seasonal Atlantic Hurricane Outlook NOAA Seasonal Atlantic Hurricane Outlook August Forecast vs. Observed: 1998-2003August Forecast vs. Observed: 1998-2003

Forecast Range Observed

Green bars indicate climatological mean andACE range for near-normal season (76%-120% of Median)

Tropical Storms Hurricanes

Major Hurricanes

1412

15

1214

135

206

76122

240

889

4

10

3

54

23

157

3188

Accumulated Cyclone Energy (ACE)

E nhanced T ropical E asterly Jet (200 -m b)

Favorable A frican E asterly Jet

E xpected C onditions A ugustE xpected C onditions A ugust --O ctober 2004O ctober 2004

H igher Pressure in U pper A tm osphere

W eaker E asterly T rade W inds (D ark B lue arrow )

W eaker E asterly T rade W inds (D ark B lue arrow )

W arm er SST sL ow er V ertical W ind Shear

and Surface Pressure(R ed A rea)

E xpected conditions during A ugust-O ctober 2004 are associated w ith the active A tlantic m ulti-decadal signal. W eak E l N iño could offset these conditions a b it.

U pper-level E asterliesE xpand W estw ard

(G reen arrow s)

Possib le E l N iño-related increase in upper-level w esterlies and vertical w ind shear

In general, for enhanced N.Atlantic Hurricane activity:

•1) We need to have Warmer SSTs of course,

•2) Westward Extended Upper level Tibetan Anticyclone (=> upper level easterlies),

•3) Lower/Easterly Vertical Wind Shear (200-850 hPa) across the North Atlantic,

•4) Favorable low-level African Easterly Jet and associated above normal cyclonic vorticity south of the jet generally favor enhanced levels of Hurricane Activity

• –--- there are significant Tropical Multidecadal (TMM) and Interannual (ENSO) influences on the activity [Chelliah and Bell(2004), Goldenberg et al (2001),..].

• Next, we examine how good are the CFS’s 200 hPa Next, we examine how good are the CFS’s 200 hPa Stream Function (representing the westward extension Stream Function (representing the westward extension of the 200 mb Tibetan Anticyclone during summer) of the 200 mb Tibetan Anticyclone during summer) forecasts in the North Atlantic and vertical Wind Shear forecasts in the North Atlantic and vertical Wind Shear (200 – 850 hPa) forecasts near the Main Development (200 – 850 hPa) forecasts near the Main Development Region (MDR) during the Aug-Sep-Oct (ASO) season Region (MDR) during the Aug-Sep-Oct (ASO) season for various forecast leads (4- through 0-month).for various forecast leads (4- through 0-month).

• --First the The Stream Function--First the The Stream Function

• --Then the Vertical Wind Shear--Then the Vertical Wind Shear

CFS Forecast of (1981-2003) Mean CFS Forecast of (1981-2003) Mean Aug-Sep-Oct 200 mb STRMFn Aug-Sep-Oct 200 mb STRMFn

at 3 different Leadsat 3 different Leads

4 Mon Lead (made from ICs in MAR)

0 Mon Lead (made from ICs in JUL)

2 Mon Lead (made from ICs in MAY)

REANL

1981 - 2003 Mean of Aug-Sep-Oct (ASO)1981 - 2003 Mean of Aug-Sep-Oct (ASO)200 mb Stream Function200 mb Stream Function

NCEP/NCAR NCEP/NCAR ReanalysisReanalysis

CFS Forecast CFS Forecast (4 Mon (4 Mon Lead)Lead)

MDR

Interdecadal/Interannual Variability Interdecadal/Interannual Variability of area (N.Atl) averaged 200 mb STRMFn ANOM of area (N.Atl) averaged 200 mb STRMFn ANOM

in the CFS Forecasts and REANLin the CFS Forecasts and REANL

1981

200390W 0E

Time Series of Forecast and Observed Area averaged Time Series of Forecast and Observed Area averaged 200mb Stream Function near the MDR200mb Stream Function near the MDR

and ACE (North Atl. Hurr. Activity)and ACE (North Atl. Hurr. Activity)

CFS FORECASTS of 200 mb STRMFN ANOM CFS FORECASTS of 200 mb STRMFN ANOM during contrasting seasons during contrasting seasons

of N.Atlantic Hurricane Activity - of N.Atlantic Hurricane Activity - 1995/19971995/1997

1995

Active N.Atlantic

Hurricane Season

1997

(Major El Nino)

Inactive Season

StrmFn ANOMS +ve

StrmFn ANOMS -ve

CFS FORECASTS of 200 mb STRMNFn ANOM CFS FORECASTS of 200 mb STRMNFn ANOM during contrasting seasons during contrasting seasons

of N.Atlantic Hurricane Activity - of N.Atlantic Hurricane Activity - 2002/20032002/2003

2003 Active

Hurricane Season

2002 (Minor El Nino) Inactive Normal

Hurricane Season

StrmFn ANOMS -ve

Next, Next, Vertical Wind ShearVertical Wind Shear

(1981 – 2003) Mean Aug-Sep-Oct (ASO)(1981 – 2003) Mean Aug-Sep-Oct (ASO)vertical Wind Shear(200-850 mb)vertical Wind Shear(200-850 mb)

CFS Forecast CFS Forecast (4 Mon (4 Mon Lead)Lead)

NCEP/NCARReanal

ysisMDR

CFS Forecast of Aug-Sep-Oct vertical Wind ShearCFS Forecast of Aug-Sep-Oct vertical Wind Shearat 3 different Leadsat 3 different Leads

as compared to Reanalysisas compared to Reanalysis

4 Mon Lead (made from ICs in MAR)

2 Mon Lead (made from ICs in MAY)

0 Mon Lead (made from ICs in JUL)

REANL

The bias in the CFS Fcsts over MDR improves with time

Interdecadal/Interannual Variability Interdecadal/Interannual Variability of area (N.Atl) averaged vertical Wind Shear of area (N.Atl) averaged vertical Wind Shear

in the CFS Forecasts and REANLin the CFS Forecasts and REANL

1995

1981

2003

Time Series of Forecast and Observed Time Series of Forecast and Observed Area averaged Vertical Wind Shear Area averaged Vertical Wind Shear and ACE (North Atl. Hurr. Activity)and ACE (North Atl. Hurr. Activity)

CFS FORECASTS of vertical Wind Shear ANOM CFS FORECASTS of vertical Wind Shear ANOM during contrasting seasons during contrasting seasons

of N.Atlantic Hurricane Activity - of N.Atlantic Hurricane Activity - 1995/19971995/1997

1995

Active N.Atlantic Hurricane

Season

1997

(Major El Nino)

Inactive Season

CFS Forecast REANL

Negative ANOM

Positive ANOM

CFS FORECASTS of vertical Wind Shear ANOM CFS FORECASTS of vertical Wind Shear ANOM during contrasting seasons during contrasting seasons

of N.Atlantic Hurricane Activity - of N.Atlantic Hurricane Activity - 2002/20032002/2003

2002 (Minor El Nino)

Inactive-Near Normal

Hurricane Season

2003

Active

Hurricane Season

CFS Forecast REANL

Negative ANOM

Positive ANOM

CFS Forecast CFS Forecast for 2004 N.Atl.Hurricane Season ??for 2004 N.Atl.Hurricane Season ??

SummarySummary

The Assessment so far ----->>>>>The Assessment so far ----->>>>>

• CPC (along with scientists from NHC and HRD) issues CPC (along with scientists from NHC and HRD) issues the North Atlantic Hurricane Outlook in early May and the North Atlantic Hurricane Outlook in early May and an update in early August bases on the subjective an update in early August bases on the subjective evaluation of the TMM and the ENSO. CCA methods evaluation of the TMM and the ENSO. CCA methods are also used to forecast future atmospheric states are also used to forecast future atmospheric states during the hurricane season. during the hurricane season.

• CFS’s seasonal long lead dynamical forecasts of CFS’s seasonal long lead dynamical forecasts of stream function, vertical wind shear, and low level stream function, vertical wind shear, and low level tropical easterly jet in the North Atlantic appear to be tropical easterly jet in the North Atlantic appear to be useful. useful.

• The CFS forecasts will definitely help CPC with the The CFS forecasts will definitely help CPC with the May/August updates of the Official NOAA outlooks of May/August updates of the Official NOAA outlooks of the N.Atlantic (and East Pacific Hurricane) Outlook(s). the N.Atlantic (and East Pacific Hurricane) Outlook(s).