The last (and my favorite) of the major hurricane seasonal forecasts came out yesterday. Phil Klotzbach and Bill Gray from Colorado State are sticking with their April forecast. Rather anti-climactic, but perhaps it’s a measure of the confidence in the forecast. I didn’t have a chance to write up something in April, so I’ll do it now before normalcy, if it sets in, brings six weeks of inactivity.
http://hurricane.atmos.colostate.edu/Forecasts is used in most of the following. My comments are in italics.
EXTENDED RANGE FORECAST OF ATLANTIC SEASONAL HURRICANE ACTIVITY AND LANDFALL STRIKE PROBABILITY FOR 2011
We continue to foresee well above-average activity for the 2011 Atlantic hurricane season. We are predicting the same levels of activity that were forecast in early April due to the combination of expected neutral ENSO conditions and very favorable atmospheric and oceanic conditions in the tropical Atlantic. We continue to anticipate an above-average probability of United States and Caribbean major hurricane landfall.
Note – in the table below, I changed K&G’s June numbers to the range that include ±1 standard deviation of their hindcast error and added a column with NOAA’s forecast.
|Forecast Parameter and 1950-2000
Climatology (in parentheses)
8 December 2010
6 April 2011
1 June 2011
|Named Storms (NS) (9.6)||17||16||12.3 – 19.7||12-18|
|Named Storm Days (NSD) (49.1)||85||80||59.9 – 101.1|
|Hurricanes (H) (5.9)||9||9||6.9 – 11.1||6-10|
|Hurricane Days (HD) (24.5)||40||35||24.8 – 45.2|
|Major Hurricanes (MH) (2.3)||5||5||3.4 – 6.6||3-6|
|Major Hurricane Days (MHD) (5.0)||10||10||4.7 – 15.3|
|Accumulated Cyclone Energy (ACE) (96.1)||165||160||112 – 212|
|Net Tropical Cyclone Activity (NTC) (100%)||180||175||127 – 223|
PROBABILITIES FOR AT LEAST ONE MAJOR (CATEGORY 3-4-5) HURRICANE LANDFALL ON EACH OF THE FOLLOWING COASTAL AREAS:
- Entire U.S. coastline – 72% (average for last century is 52%)
- U.S. East Coast Including Peninsula Florida – 48% (average for last century is 31%)
- Gulf Coast from the Florida Panhandle westward to Brownsville – 47% (average for
last century is 30%)
PROBABILITY FOR AT LEAST ONE MAJOR (CATEGORY 3-4-5) HURRICANE TRACKING INTO THE CARIBBEAN (10-20°N, 60-88°W)
- 61% (average for last century is 42%)
This year’s forecasts are funded by private and personal funds. We thank the GeoGraphics Laboratory at Bridgewater State College (MA) for their assistance in developing the United States Landfalling Hurricane Probability Webpage (available online at http://www.e-transit.org/hurricane).
The forecast is a blend of a statistical analysis, a search for analog years with similarities to April-May conditions and the expected August-October conditions, and “qualitative adjustments for other factors not explicitly contained in any of these schemes.”
As they often do, the June forecast is based on a new June statistical model and uses just four predictors (the geographic ranges are in the image at the top):
|Predictor||2011 Forecast Value|
|1) April-May SST (15-55°N, 15-35°W) (+)||+0.3 SD|
|2) April-May 200 MB U (0-15°S, 150°E-20°W) (+)||+1.6 SD|
|3) ECMWF 1 May SST Forecast for September Nino 3 (5°S-5°N, 90-150°W) (-)||+0.3 SD|
|4) May SLP (20-40°N, 30-50°W) (-)||-0.9 SD|
Decoding key: SST: Sea Surface Temperature; SLP: Sea Level Pressure, SD: Standard deviation; 200 MB U: zonal wind at atmospheric pressure 200 mb, an altitude of about 40,000 feet.
The moderate-to-strong La Niña conditions of this past winter have continued to weaken since early April. According to the Climate Prediction Center (CPC), SST anomalies in the central and eastern tropical Pacific have now warmed to the point where ENSO is in its neutral state. While the moderation of tropical Pacific SSTs have continued over the past couple of months, we do not expect to see a transition to El Niño conditions during the next several months.
Current Atlantic Basin Conditions
Conditions in the Atlantic remain favorable for an active season. May SSTs across the tropical Atlantic remain at above-average levels (Figure 17). The anomalously strong trades during the latter part of the winter that caused some anomalous cooling in the tropical Atlantic have now weakened (Figure 18). Sea level pressure anomalies during the month of May were also well below-average throughout the tropical Atlantic (Figure 19). Altogether, tropical Atlantic conditions currently reflect an environment conducive for an active hurricane season.
Forthcoming Updated Forecasts of 2011 Hurricane Activity
We will be issuing a final seasonal updates of our 2011 Atlantic basin hurricane forecast on Wednesday, 3 August. We will also be issuing two-week forecasts for Atlantic TC activity during the climatological peak of the season from August-October. A late-season forecast for the Caribbean will be issued in early October. A verification and discussion of all 2011 forecasts will be issued in late November 2011. All of these forecasts will be available on the web at: http://hurricane.atmos.colostate.edu/Forecasts.
I will likely report on the Aug. 3rd update, but will probably not cover the two-week forecasts. Last year, several were dominated by current activity, low or high.