NOAA 2015 Updated Atlantic Hurricane Season Outlook Dr. Gerry Bell Lead Seasonal Forecaster Climate Prediction Center/ NOAA/ NWS Collaboration With National Hurricane Center/ NOAA/ NWS Hurricane Research Division/ NOAA/ OAR 1
NOAA s 2015 Atlantic Hurricane Season Outlooks Reasons for higher likelihood of below-normal season compared to May outlook: Significant El Niño, exceptionally unfavorable conditions now in place Atlantic SSTs are even colder relative to the global tropics than expected 4
The 2015 Atlantic Outlooks in a Historical Perspective Caption: Seasonal Accumulated Cyclone Energy (ACE) index during 1950-2014 (Blue bars) and NOAA s 2015 outlook ranges with a 70% probability of occurrence (Red bars). Shading indicates NOAA s thresholds for classifying hurricane season strength. Green line indicates lower threshold for a very active season. NOAA s updated 2015 Atlantic hurricane season outlook indicates a 70% probability of an ACE range of 25%-70% of the median. ACE index measures overall season strength by accounting for the combined intensity and duration of tropical storms and hurricanes. ACE=Sum of squares of maximum sustained surface wind speed (measured 6-hourly) for all named storms while at least tropical storm strength. 5
Recent Evolution of Equatorial Pacific SST Departures ( o C) During September-December 2014, positive SST anomalies covered most of the equatorial Pacific. During January through mid-march 2015, near-to-below average SSTs were observed in the eastern Pacific, and positive SST anomalies persisted across the western and central Pacific. Since April 2015, positive SST anomalies strengthened across the east-central Pacific.
Niño Region SST Departures ( o C) Recent Evolution The latest weekly SST departures are: Niño 4 Niño 3.4 Niño 3 Niño 1+2 1.1ºC 2.2ºC 2.3ºC 2.0ºC
SST Departures ( o C) in the Tropical Pacific During the Last Four Weeks During the last four weeks, equatorial SSTs were above average across the central and eastern Pacific, with the largest anomalies in the east-central Pacific.
Global SST Departures ( o C) During the Last Four Weeks During the last four weeks, equatorial SSTs were above average across the central and eastern Pacific and the Indian Ocean, and below average in the Atlantic Ocean.
Tropical OLR and Wind Anomalies During the Last 30 Days Negative OLR anomalies (enhanced convection and precipitation) were evident across the central and eastern tropical Pacific. Positive OLR anomalies (suppressed convection and precipitation) were observed over Indonesia, the Philippines, and Papua New Guinea. Anomalous low-level (850-hPa) westerly winds extended from the western to the east-central equatorial Pacific. Anomalous upper-level (200-hPa) easterlies persisted in the western and central equatorial Pacific. An anomalous anti-cyclonic couplet straddled the equator over the east-central tropical Pacific. A A
Outgoing Longwave Radiation (OLR) Anomalies During early March, negative OLR anomalies shifted from Indonesia to the Date Line, where they persisted until late May. Since early May, negative anomalies have persisted in the central and/or eastern Pacific. Since early July, positive anomalies have persisted near Indonesia. Drier-than-average Conditions (orange/red shading) Wetter-than-average Conditions (blue shading)
CPC/IRI Probabilistic ENSO Outlook Updated: 13 August 2015 The chance of El Niño is greater than 90% through Northern Hemisphere winter and is near 70% through spring (MAM) 2016.
IRI/CPC Pacific Niño 3.4 SST Model Outlook Almost all of the models indicate Niño 3.4 SST anomalies will remain greater than or equal to +0.5ºC through spring 2016. All multi-model averages indicate that Niño 3.4 will be above +1.5ºC (a strong El Niño) during late 2015 into early 2016. Figure provided by the International Research Institute (IRI) for Climate and Society (updated 18 August 2015).
Vertical Wind Shear: Total and Anomalies Last 30 days Vertical wind shear is well above average (Blue) across the MDR.
Very high shear expected this hurricane season over the deep tropical Atlantic