FXPN30 KWNC 221405
PMDEPH
EASTERN NORTH PACIFIC HURRICANE SEASON OUTLOOK 2009
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
1100 AM EST THU 21 MAY 2009
 
 
NOTE: FIGURES MENTIONED IN THE DISCUSSION ARE AVAILABLE
ON THE INTERNET AT HTTP://WWW.CPC.NCEP.NOAA.GOV
 
THE EASTERN PACIFIC HURRICANE SEASON OUTLOOK IS AN OFFICIAL
PRODUCT OF THE NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
/NOAA/ CLIMATE PREDICTION CENTER /CPC/, AND IS PRODUCED IN
COLLABORATION WITH SCIENTISTS FROM THE NOAA NATIONAL HURRICANE
CENTER /NHC/.
INTERPRETATION OF NOAAS EASTERN PACIFIC SEASONAL HURRICANE
OUTLOOK
1. PREPAREDNESS
THIS OUTLOOK PROVIDES THE PUBLIC WITH A GENERAL GUIDE TO THE
EXPECTED OVERALL ACTIVITY FOR THE UPCOMING HURRICANE SEASON. IT
IS NOT A SEASONAL HURRICANE LANDFALL FORECAST, AND IT DOES
NOT IMPLY LEVELS OF ACTIVITY FOR ANY PARTICULAR REGION.
HURRICANE DISASTERS CAN OCCUR WHETHER THE SEASON IS ACTIVE
OR QUIET. RESIDENTS, BUSINESSES, AND GOVERNMENT AGENCIES
OF COASTAL AND NEAR-COASTAL REGIONS SHOULD PREPARE FOR EVERY
HURRICANE SEASON REGARDLESS OF THE SEASONAL OUTLOOK. NOAA, FEMA,
THE NHC, SMALL BUSINESS ADMINISTRATION, AND THE RED CROSS ALL
PROVIDE IMPORTANT HURRICANE PREPAREDNESS INFORMATION ON THEIR
WEB SITES. IT ONLY TAKES ONE HURRICANE /OR EVEN TROPICAL STORM/
TO CAUSE A DISASTER.
2. NOAA DOES NOT MAKE SEASONAL HURRICANE LANDFALL PREDICTIONS
NOAA DOES NOT MAKE HURRICANE LANDFALL PREDICTIONS ON A SEASONAL
TIMESCALE. HURRICANE LANDFALLS ARE LARGELY DETERMINED BY THE
WEATHER PATTERNS IN PLACE AS THE HURRICANE APPROACHES, WHICH
ARE NOT PREDICTABLE MORE THAN 5-7 DAYS IN ADVANCE.
3. NATURE OF THIS OUTLOOK AND THE "LIKELY" RANGES OF ACTIVITY
THIS OUTLOOK IS PROBABILISTIC, MEANING THE STATED "LIKELY"
RANGES OF ACTIVITY HAVE A CERTAIN LIKELIHOOD OF OCCURRING. THESE
RANGES ARE TYPICALLY SEEN IN 2 OF 3 SEASONS WITH SIMILAR CLIMATE
CONDITIONS AND UNCERTAINTIES TO THOSE EXPECTED THIS YEAR.
THESE LIKELY RANGES DO NOT REPRESENT THE TOTAL RANGES OF
ACTIVITY SEEN IN PAST SEASONS HAVING SIMILAR CLIMATE CONDITIONS
TO THOSE EXPECTED THIS YEAR, BUT ARE SIMPLY THE MOST LIKELY.
THE OUTLOOK IS BASED ON PREDICTIONS OF LARGE-SCALE CLIMATE
FACTORS KNOWN TO BE STRONG INDICATORS OF UPCOMING SEASONAL
EASTERN PACIFIC HURRICANE ACTIVITY, AND TAKES INTO ACCOUNT
UNCERTAINTIES INHERENT IN SUCH CLIMATE OUTLOOKS /SEE ITEM
4 BELOW/
4. THREE MAJOR SOURCES OF UNCERTAINTY IN THE SEASONAL OUTLOOKS
EL NINO AND LA NINA FORECASTS ARE PRESENTLY THE BIGGEST SOURCE
OF UNCERTAINTY FOR THE HURRICANE OUTLOOK. THE PERIOD BETWEEN
MARCH - JULY IS REFERRED TO AS THE "SPRINGTIME FORECAST
BARRIER," A PERIOD WHEN PREDICTING THESE PHENOMENA CAN BE
DIFFICULT BECAUSE THE ATMOSPHERE IS IN A STATE OF TRANSITION.
MANY COMBINATIONS OF NAMED STORMS AND HURRICANES CAN OCCUR
FOR THE SAME SET OF CLIMATE CONDITIONS. ONE CANNOT KNOW WITH
CERTAINTY WHETHER A GIVEN CLIMATE SIGNAL WILL BE ASSOCIATED WITH
SEVERAL SHORT-LIVED STORMS OR FEWER LONGER-LIVED STORMS WITH
GREATER INTENSITY.  WEATHER PATTERNS THAT ARE UNPREDICTABLE
ON SEASONAL TIME SCALES CAN SOMETIMES DEVELOP AND LAST FOR
WEEKS OR MONTHS, POSSIBLY AFFECTING SEASONAL HURRICANE ACTIVITY.
2009 EASTERN PACIFIC HURRICANE OUTLOOK SUMMARY
THE CLIMATE PREDICTION CENTERS 2009 EASTERN PACIFIC HURRICANE
SEASON OUTLOOK CALLS FOR AN 80 PERCENT CHANCE OF A NEAR-
TO BELOW-NORMAL SEASON.  BECAUSE OF UNCERTAINTIES IN CURRENT
PREDICTIONS FOR EL NINO, A NEAR-NORMAL AND BELOW-NORMAL SEASON
ARE EQUALLY LIKELY AT THIS TIME. THE OUTLOOK ALSO INDICATES A 20
PERCENT CHANCE OF AN ABOVE-NORMAL SEASON. SEE NOAA DEFINITIONS
OF ABOVE, NEAR-, AND BELOW-NORMAL SEASONS.
THIS OUTLOOK IS BASED ON THE ANALYSIS AND PREDICTION OF TWO
MAIN CLIMATE SIGNALS:
1. THE ONGOING CONDITIONS THAT HAVE BEEN SUPPRESSING EASTERN
PACIFIC HURRICANE SEASONS SINCE 1995, AND 2. EITHER ENSO-NEUTRAL
CONDITIONS OR EL NINO.
CLIMATE PATTERNS SIMILAR TO THOSE EXPECTED THIS YEAR HAVE
HISTORICALLY PRODUCED A WIDE RANGE OF ACTIVITY. ALLOWING FOR
UNCERTAINTIES, WE ESTIMATE A 70 PERCENT CHANCE OF OCCURRENCE
FOR EACH OF THE FOLLOWING RANGES OF ACTIVITY:
13- 18 NAMED STORMS, 6- 10 HURRICANES, 2- 5 MAJOR HURRICANES,
AN ACE RANGE OF 70 PERCENT-130 PERCENT OF THE MEDIAN
THESE LIKELY RANGES HAVE BEEN OBSERVED IN ABOUT 70 PERCENT
OF PAST SEASONS HAVING SIMILAR CLIMATE CONDITIONS TO THOSE
EXPECTED THIS YEAR. THEY DO NOT REPRESENT THE TOTAL RANGES OF
ACTIVITY SEEN IN THOSE PAST SEASONS.
THE EASTERN PACIFIC HURRICANE REGION COVERS THE EASTERN PACIFIC
OCEAN EAST OF 140OW NORTH OF THE EQUATOR.
THERE WILL BE NO FURTHER UPDATES TO THIS OUTLOOK.
DISCUSSION
1. EXPECTED 2009 ACTIVITY
THIS OUTLOOK IS A GENERAL GUIDE TO THE EXPECTED OVERALL ACTIVITY
FOR THE 2009 EASTERN PACIFIC HURRICANE SEASON. IT IS NOT A
SEASONAL HURRICANE LANDFALL FORECAST, AND IT DOES NOT IMPLY
LEVELS OF ACTIVITY FOR ANY PARTICULAR AREA.
THE CLIMATE FACTORS EXPECTED TO GUIDE THE 2009 HURRICANE SEASON
ARE 1/ THE CONTINUATION OF CONDITIONS THAT HAVE BEEN SUPPRESSING
ACTIVITY SINCE 1995, AND 2/ EITHER ENSO-NEUTRAL /NO EL NINO OR
LA NINA/ CONDITIONS OR EL NINO DURING THE PEAK /JULY-SEPTEMBER/
OF THE SEASON.
HISTORICALLY, SEASONS WITH CLIMATE PATTERNS SIMILAR TO THOSE
EXPECTED THIS YEAR HAVE PRODUCED A WIDE RANGE OF ACTIVITY. THIS
OUTLOOK CONSIDERS THE HISTORICAL DISTRIBUTION OF ACTIVITY FOR
THESE CLIMATE FACTORS, UNCERTAINTIES IN WHETHER EL NINO WILL
DEVELOP, AND THE POSSIBILITY OF OTHER UNPREDICTABLE FACTORS ALSO
INFLUENCING THE SEASON. BASED ON THESE FACTORS, WE ESTIMATE AN
80 PERCENT CHANCE OF A NEAR-NORMAL TO BELOW-NORMAL HURRICANE
SEASON /40 PERCENT CHANCE OF EACH/, AND A 20 PERCENT CHANCE
OF AN ABOVE-NORMAL SEASON.
AN IMPORTANT MEASURE OF TOTAL SEASONAL ACTIVITY IS NOAAS
ACCUMULATED CYCLONE ENERGY /ACE/ INDEX, WHICH ACCOUNTS FOR
THE COLLECTIVE STRENGTH AND DURATION OF TROPICAL STORMS AND
HURRICANES DURING THE SEASON. THE ACE INDEX IS ALSO USED TO
DEFINE THE SEASON TYPE. A VALUE OF 92 PERCENT-138 PERCENT OF
THE MEDIAN /MEDIAN VALUE IS 109/ DEFINES A NEAR-NORMAL SEASON.
BASED ON THE ABOVE FACTORS, WE ESTIMATE A 70 PERCENT CHANCE
THAT THE 2009 SEASONAL ACE RANGE WILL BE 70 PERCENT-130 PERCENT
OF THE MEDIAN. THIS RANGE CAN BE SATISFIED EVEN IF THE NUMBERS
OF NAMED STORMS, HURRICANES, OR MAJOR HURRICANES FALL OUTSIDE
THEIR LIKELY RANGES.
THE LIKELY /70 PERCENT CHANCE/ RANGES OF ACTIVITY FOR 2009 ARE:
13-18 NAMED STORMS, 6-10 HURRICANES, AND 2-5 MAJOR HURRICANES.
2. THE ONGOING LOW-ACTIVITY HURRICANE ERA IN THE EASTERN PACIFIC
THE EASTERN PACIFIC HAS SEEN GENERALLY SUPPRESSED HURRICANE
ACTIVITY SINCE 1995. DURING 1995-2008, 64 PERCENT OF SEASONS
WERE BELOW NORMAL, 29 PERCENT WERE NEAR NORMAL, ONLY ONE WAS
ABOVE NORMAL. THESE SEASONS AVERAGED ABOUT 14 NAMED STORMS,
7 HURRICANES, AND 3 MAJOR HURRICANES, WITH AN ACE VALUE
OF 80 PERCENT OF THE MEDIAN. THIS VALUE FALLS WITHIN NOAAS
DEFINITION FOR A BELOW-NORMAL SEASON. DURING THIS LOW-ACTIVITY
ERA, ONLY THE STRONG EL NINO OF 1997 PRODUCED AN ABOVE-NORMAL
SEASON. THIS ONGOING LOW-ACTIVITY ERA IS THE MAIN REASON WE
EXPECT THE 2009 HURRICANE SEASON TO BE NEAR- OR BELOW- NORMAL.
THESE CONDITIONS CONTRAST WITH THE PREVIOUS HIGH-ACTIVITY
ERA /1982-1994/ IN THE EASTERN PACIFIC, IN WHICH 62 PERCENT
OF HURRICANE SEASONS WERE ABOVE NORMAL, 31 PERCENT WERE NEAR
NORMAL, AND ONLY ONE WAS BELOW NORMAL. THESE SEASONS AVERAGED
18.2 NAMED STORMS, 10.8 HURRICANES, AND 5.6 MAJOR HURRICANES,
WITH AN ACE VALUE OF 157 PERCENT OF THE MEDIAN. THIS VALUE FALLS
WITHIN NOAAS DEFINITION FOR AN ABOVE-NORMAL SEASON. DURING THIS
PERIOD, 5 OF 8 EL NINO EPISODES LED TO AN ABOVE-NORMAL SEASON,
AND ONLY 1988 WAS CATEGORIZED AS BELOW-NORMAL, DUE TO A STRONG
LA NINA.
3. ENSO
THE EL NINO/ SOUTHERN OSCILLATION /ENSO/ IS AN IMPORTANT
CLIMATE PREDICTOR FOR EASTERN PACIFIC HURRICANE ACTIVITY. EL
NINO GENERALLY PRODUCES CONDITIONS THAT ARE MORE CONDUCIVE
TO HURRICANE ACTIVITY, WHILE LA NINA SUPPRESSES THE
ACTIVITY. HOWEVER, THESE TYPICAL IMPACTS CAN BE STRONGLY
MODULATED BY CONDITIONS ASSOCIATED WITH A LOW- OR HIGH-ACTIVITY
ERA.
LA NINA DISSIPATED DURING APRIL 2009, AND CURRENT SEA-SURFACE
TEMPERATURE ANOMALIES IN THE EAST-CENTRAL EQUATORIAL PACIFIC
ARE NEAR AVERAGE. NOAA DEFINES THESE CONDITIONS AS ENSO-NEUTRAL.
THERE IS CONSIDERABLE SPREAD AND UNCERTAINTY IN THE CLIMATE
MODELS REGARDING THE EVOLUTION OF ENSO DURING THE NEXT
SEVERAL MONTHS, AND MOST OF THE MODELS HAVE HISTORICALLY SHOWN
LITTLE-TO-NO SKILL AT THIS TIME OF THE YEAR. THE MOST RECENT
DYNAMICAL MODEL FORECASTS SUGGEST EL NINO WILL DEVELOP DURING
THE SUMMER, ALTHOUGH THERE IS CONSIDERABLE DISAGREEMENT AS
TO ITS STRENGTH. IN CONTRAST, ALL OF THE RECENT STATISTICAL
MODEL FORECASTS SUGGEST ENSO-NEUTRAL CONDITIONS WILL PREVAIL.
THE SEASONAL HURRICANE OUTLOOK REFLECTS THE POSSIBILITY OF
EL NINO DEVELOPING AND BECOMING STRONG ENOUGH TO IMPACT THE
SEASON. HOWEVER, BECAUSE OF THE ONGOING LOW-ACTIVITY ERA,
THE HISTORICAL DATA SUGGESTS THESE IMPACTS WOULD MOST LIKELY
RAISE THE ACTIVITY INTO THE NEAR-NORMAL RANGE. HOWEVER,
SOME DYNAMICAL MODEL SIMULATIONS PREDICT SIGNIFICANT EL
NINO-RELATED CIRCULATION ANOMALIES TO DEVELOP THIS SUMMER,
WOULD LEAVES OPEN THE POSSIBILITY /20 PERCENT CHANCE/ OF AN
ABOVE-NORMAL SEASON. A BELOW-NORMAL SEASON IS MORE LIKELY IF
ENSO-NEUTRAL CONDITIONS PERSIST, AND A NEAR-NORMAL SEASON IS
MORE LIKELY IF EL NINO DEVELOPS.
 
$$