# Presentation: 641388

**2003 Atlantic Hurricane Season Summary**
**By**
**Gerald Bell, Muthuvel Chelliah**
**Climate Prediction Center NOAA/ NWS**

**And **
**NOAA Atlantic Hurricane forecast team members**
**Dr. Chris Landsea****1****, Stanley Goldenberg****1****, **
**Dr. Richard Pasch****2****, Eric Blake****2**
**	****  ****1 Hurricane Research Division/ NOAA/ OAR**
**                ****2 National Hurricane Center/ NOAA/ NWS**

## Outline

**Season statistics**
**Total seasonal activity**
**Rainfall from U.S. landfalling tropical systems**
**Atmospheric circulation**
**Ongoing active decadal signal**
**NOAA Atlantic Hurricane Outlooks**
**Summary**

## 2003 Atlantic Hurricane Season Statistics

**2003 Atlantic Hurricane Season Statistics**

**       ****Observed                                                             **
**Above Normal**
**                                               **
**14 Tropical Storms**
** ****6  Hurricanes**
** ****3  Major Hurricanes**
**180.5 % ACE Index (% median)**

**       ****Observed                                                      NOAA Prediction**
**                                                **_**Season Type          May 23      August 7**_
**Above Normal****                  Above Normal         ****55%           60%**
**                                                ****Near Normal           35%            35%**
**                                                ****Below Normal         10 %             5%**
**                                                 **
**14 Tropical Storms                                                11-15           12-15                **
** ****6  Hurricanes                                                           6-9              7-9                      **
** ****3  Major Hurricanes                                                2-4              3-4                      **
**183 % ACE Index (% median)                         110-180%   120-170%   **

## Main Development Region (MDR)

**Main Development Region (MDR)**

**MDR is defined as tropical Atlantic and Caribbean Sea between 9****o****-21.5****o****N**
**During 1949-2002 Tropical Systems first named in MDR account for:**
**71% of the 53-year total activity measured by ACE index**
**55% of all hurricanes**
**79% of all major hurricanes**
**Nine-fold drop in activity in MDR between above- and below-normal seasons**

## 2003 Named Storm Tracks

**Figure Courtesy of Unisys.com**

**Main Development Region**

## 2003 Atlantic Tropical Systems By Region Where First Named

**2003 Atlantic Tropical Systems ****By Region Where First Named**

**        ****Tropical               Hurricanes            Major**
**          ****Storms                                           Hurricanes **

## Total Seasonal Activity 

_**Total seasonal activity**_**: Collective strength and duration of tropical storms and hurricanes**
**More representative of overall activity than seasonal numbers systems**
**NOAA’s **_**A**_**ccumulated **_**C**_**yclone **_**E**_**nergy (ACE) Index:**
**Wind energy index defined as sum of squares of 6-hourly maximum sustained wind speed for all systems while at least tropical storm strength. Similar to HDP index ( Gray et al., CSU).**
**ACE is highly predictable and dominated by activity in MDR**
**Key forecast parameter for NOAA hurricane outlooks**
**Used to classify seasons: above normal, near normal, below normal**

## Historical Perspective: ACE Index

**Active Decades **
**ACE = 114**
**10 TS, 6.5 H, 3 MH**

**Above **
**Normal**
**Season **

**Near**
**Normal **

**Below **
**Normal**
**Season**

**65**

**103**

**2003**

**Historical Perspective: ACE Index**

**       ****Atlantic Basin            Main Development Region**

**   ****Active Decade **
**     ****ACE = 134**
**13 TS, 8 h, 3.6 MH **

**IN-active Decades ACE = 65**
** ****9 TS, 5 H, 1.5 MH**

**2003 Predicted Range**

## 2003 ACE Index for storms first named in specified region

**2003 ACE Index for storms ****first named in specified region**

## 2003 ACE Index by Storm

**2003 ACE Index by Storm**

## U.S. Rainfall TotalsLandfalling Tropical Systems

**6 named storms made landfall in U.S. during 2003**
**4 formed over Gulf of Mexico**
**2 formed in MDR**
**1 hit as tropical depression (Henri)**
**3 hit as tropical storms (Bill, Grace, Erika)**
**2 hit as hurricanes (Claudette, Isabel)**

## Storm Precipitation Totals (mm)

**TS Bill  (G. Mexico)**
**30 Jun - 1 Jul**

**Hurricane Claudette (MDR) **
**15-16 July**

## Storm Precipitation Totals (mm)

**TS Grace (G. Mexico)**
**31 August**

**TS Erika (G. Mexico) **
**16-17 August**

## Storm Precipitation Totals (mm)

**Storm Precipitation Totals (mm)**

**TS Henri  (G. Mexico)**
**6 Sep**

**Hurricane Isabel (MDR) **
**18-19 Sep**

## Precipitation (mm): 30 Jun – 9 Oct

**Precipitation (mm): 30 Jun – 9 Oct**

**Total Precipitation during landfall days**

**Percent of Period Total Precip by landfall days**

## 2003 Aug-Sep Mean Atmospheric Conditions

## Atlantic Weekly SST Departures (oC)

**Atlantic Weekly SST Departures (****o****C)**

## Height and Anomalies (shading)August-September

**200-hPa**

**1000-hPa**

**Lower Surface**
**Pressure**

**Stronger **
**Subtropical **
**Ridge**

## 200-850 hPa Anomalous Vertical Wind Shear August-September 2003

**Lower Shear**

**Anomalous Shear of Zonal Wind**

**Anomalous Strength of Vertical Shear**

**Anomalous Easterly**
** ****Shear,**
**Stronger Tropical **
**Easterly Jet**

## 700-hPa Rel. Vort. (shading), Zonal Wind (contour)

**700-hPa Rel. Vort. (shading), Zonal Wind (contour)**

**African Easterly Jet **
**axis north of normal**
**Cyclonic Shear (shading)**

**Cyclonic Anoms (Red)**
**Westerly Anoms**

**Aug-Sep 2003 Mean**

## Ongoing Decadal Signal

## 200-850 hPa Anomalous Vertical Shear of Zonal Wind: Aug-Sep.

**200-850 hPa Anomalous Vertical Shear of Zonal Wind: Aug-Sep.**

**Lower Shear**

**Higher Shear**

**Averaging**
**Region**

** ****1980         1985          1990       1995         2000**

**M/S**
**-8   –6   –4   -2   0     2    4**

## 700-hPa Zonal Wind Anomalies Aug-Sep

**700-hPa Zonal Wind Anomalies**** Aug-Sep**

** ****1980        1985           1990          1995          2000**

**Averaging **
**Region**

**M/S**
**–****2 –1   0   1  2   3   4**

## Anomalous 700-hPa Relative Vorticity:Equatorward flank of African Easterly Jet Aug-Sep

**Anomalous 700-hPa Relative Vorticity:****Equatorward flank of African Easterly Jet**** Aug-Sep**

**Anticyclonic**

**Cyclonic**

** ****1980        1985         1990       1995        2000**

**x 10****-6****  S****-1**
**-4  –2    0     2    4    6    8**

**Averaging **
**Region**

## NOAA Atlantic Hurricane Outlooks

## Climate Links to Tropics 

**Tropical convection is dominant forcing of coherent circulation anomalies associated with seasonal and decadal extremes in Atlantic hurricane activity.  (Bell and Chelliah 2004)**
**Dominant Climate factors:**
**ENSO (Gray (1984): **
**Tropical multi-decadal mode (TMM): Chelliah and Bell (2003)**

## NOAA’s Atlantic Hurricane Outlooks Forecast Procedure

** **
**	****Use EOF regressions and analogue/ binning techniques to**
**	****predict upcoming atmospheric conditions and activity in MDR**
**	**
**	****Analysis of the combined modes is critical to the forecast**
**	**
**2. Observed Apr-May, Jun-Jul anomalies to predict ASO activity**
**Analogue years, bin with respect to leading tropical modes.**
**Extended CCA forecasts of vertical shear**
**Final outlook is subjective blend of items 1-2**

**NOAA’s Atlantic Hurricane Outlooks ****Forecast Procedure**

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

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

**Forecast Range**

**Observed**

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

**Tropical Storms**

**ACE Index**

**Hurricanes**

**Major Hurricanes**

**14**

**12**

**15**

**12**

**14**

**135**

**206**

**76**

**122**

**240**

**8**

**8**

**9**

**4**

**10**

**3**

**5**

**4**

**2**

**3**

**14**

**6**

**3**

**183**

## Summary

**Above-normal 2003 Atlantic hurricane season. **
**1995-2003 most active in record**
**2. Most of  2003 activity (86% of ACE index) associated with MDR.**
**3. Ongoing decadal atmospheric signal favors active hurricane seasons.**
**4. NOAA outlooks based on prediction of ENSO and Tropical Multi-decadal Mode**
**5. Diagnosing and forecasting seasonal Atlantic hurricane variability requires an understanding of both modes, and their combined impacts.**

## 2003 Above-normal Hurricane Season Conditions

_**2003 Above-normal Hurricane Season Conditions**_

**Favorable African Easterly Jet (700-hPa) reflects**
**Northward shift of jet axis**
**Strong cyclonic shear along southern flank**

**Very Low Vertical Shear**

**Favorable African **
**Easterly Jet (700-hPa)**

**Amplified Subtropical Ridge**

**Stronger Tropical Easterly Jet (200-hPa)**

**WET**

## Extras

## 700-hPa Rel. Vort., Zonal Wind (contour)

**700-hPa Rel. Vort., Zonal Wind (contour)**

**Cyclonic**
**Westerly**

**April-May 2003 Anomalies**

**June-July 2003 Anomalies**

## 700-hPa Potential VorticityAugust-September Mean

**700-hPa Potential Vorticity****August-September Mean**

**2003**

**1997 (Inactive Season)**

**High PV in MDR,**
**Gradient Reversal Linear Instability**

**Lower PV in MDR,**
**No Gradient Reversal**

## Precipitable Water (inches), 1000-hPa WindAugust-September 2003

**High Precipitable water in MDR and West African monsoon region **