The 2009 Hurricane Season Overview Jae-Kyung Schemm Gerry Bell Climate Prediction Center NOAA/ NWS/ NCEP 1
Overview outline 1. Current status for the Atlantic, Eastern Pacific and Western Pacific basins 2. CPC hurricane season outlooks 3. Climate factors influencing this season 4. Summary
Atlantic TC Tracks During 2009 Out of 8 named storms, 5 formed in the MDR. None formed over the Caribbean Sea. Figure Courtesy of Unysis Weather
Eastern Pacific Basin TC Tracks during 2009 TCs form somewhat west of the climatological area of storm origin. 19 named storms and 7 hurricanes so far for the season
Western Pacific Basin TC Tracks during 2009 24 named storms, 8 typhoons and 4 super-typhoons as of Oct. 22
NOAA 2009 Atlantic Hurricane Season Outlooks Season and August May Activity Type Update Outlook Observed Chance Above Normal 10% 25% Chance Near Normal 50% 50% Chance Below Normal 40% 25% Named Storms (NS) 7-11 9-14 8 Hurricanes (H) 3-6 4-7 2 Major Hurricanes (MH) 1-2 1-3 2 ACE (% Median) 60%-110% 65%-130% 45% NOAA s Seasonal Hurricane Outlook is a general guide to the expected overall strength of the hurricane season. It is not a seasonal hurricane landfall forecast, and does not imply levels of activity for any particular region. We estimate a 70% probability for the stated ranges of NS, H, MH, and ACE. These ranges have been observed in about 70% of past seasons having similar climate conditions and uncertainties to those expected this year. They do not represent the total range of activity seen in those past seasons.
NOAA 2009 East Pacific Hurricane Outlook Season and 2009 Activity Type Outlook Normals Observed Chance Above Normal 20% Chance Near Normal 40% Chance Below Normal 40% Tropical Storms 13-18 15-16 19 Hurricanes 6-10 9 7 Major Hurricanes 2-5 4-5 3 ACE (% Median) 70%-130% 100% 69% Based on past seasons with similar climate conditions, we estimate a 70% probability for each range. Historically, roughly two-thirds of similar seasons had activity in these ranges.
Historical Atlantic Seasonal Activity NOAA s ACE index shows the overall strength of the hurricane season. NOAA s updated 2009 Atlantic hurricane outlook indicates a 70% chance the ACE range will be 60%-110% of the median. This range is lower than was indicated in the May outlook.
Historical East Pacific Seasonal Activity NOAA s 2009 Eas Pacific hurricane outlook (Red bar) indicates a 70% chance the ACE range will be 70%-130% of the median.
New procedures adapted for the 2009 outlooks 1. Hybrid dynamical-statistical procedure (Wang, et al., 2009) - multiple regression procedures using SST and shear forecasts from the operational CFS (T62) forecast runs. Forecast for Atlantic: 6-12 TS, 3-7 H, 1-3 MH, 40-128% ACE Forecast for E. Pacific: 14-16 TS, 7-9 H 2. Prediction based on the T382 CFS forecast runs with the cyclone detection and tracking method by Carmago and Zebiak (200). 10 member ensemble runs with mid-april ICs. Forecast for Atlantic: 7.5 TS (Clim 10.9), 75% ACE Forecast for EN Pacific: 13 TS (Clim 13), 97% ACE Forecast for WN Pacific: 21.5 TS (Clim 18.1), 144% ACE
Main Climate Factors Influencing the 2009 Atlantic Hurricane Season El Niño Minimal MJO activity to offset persistent ENSO forcing Conditions associated with ongoing high-activity era
El Niño Increased Wind Shear, Fewer Hurricanes More Shear Warm, Wet
Comparison of JAS SST anomalies for 2008 and 2009
JAS Wind shear comparison between 2008 and 2009
Anomalous 200-hPa Wind: Aug-Sep 2009 Anomalous upper-level westerly winds present across the Caribbean Sea. Anomalies are a tropical signature, with no evidence of an amplified tropical upper-tropospheric trough (TUTT) over North Atlantic Ocean. Anomalous trough across U.S. is not conducive to landfalling TCs.
Historical Time Series: Aug-Sep The area-average vertical wind shear was the strongest since the 2002 El Niño.
Key Features Blue Circles: Anticyclonic anomalies associated with El Niño Red Ovals: Global scale cyclonic anomalies (blue shading in NH, red shading in SH) Green Circles: Stronger upper-level ridge associated with enhanced west African monsoon 17 June-July 2009: Observed and Regressed 200-hPa Streamfunction Anomalies El Niño influence already present during mid-june and July. Observed anomalies reflect the ongoing Atlantic high-activity era and El Niño. Based on Bell and Chelliah (2006, J. Climate).
200-hPa: Anomalous Velocity Potential 2009 2002 2009: ENSO dominates the divergent circulation since mid-july. Only one MJO event (mid-august) was sufficiently strong to increase Atlantic hurricane activity. Much stronger MJO/ intra-seasonal activity observed during the 2002 El Niño.
Summary 1. El Niño began to significantly impact the atmospheric circulation soon after developing in mid-june. 2. The suppressed Atlantic hurricane season during 2009 is linked mainly to increased vertical wind shear over the Caribbean Sea, consistent with El Niño. 3. MJO activity was minimal, offsetting the El Niño signal only once (mid- August). 4. Conditions associated with the ongoing high-activity era in the tropical Atlantic are still present (stronger African monsoon system, warm SST anomaly and weaker trade winds in MDR). There is no indication that this period of increased activity, which began in 1995, has ended.