Dry Season Outlook: El Niño and Potential Impacts Robert Molleda Warning Coordination Meteorologist National Weather Service Miami Forecast Office

Rainy Season Summary May 11 – October 17 (160 days). Wetter (mostly) and hotter than normal. Naples and its immediate Gulf coastal areas observed below normal precipitation. Pockets of SE Florida metro areas also received below normal precipitation.

Southeast Florida Wet Season 2009 Rainfall

Southwest Florida Wet Season 2009 Rainfall

Lake Okeechobee Level

El Niño: What Does It Mean For South Florida This Winter?

Climate is what we expect, weather is what we get. Mark Twain Transition Zone Between Two MajorClimates Florida - Prone to Very High Climate and Weather Variability Slide Courtesy: NWS Melbourne, FL

Strong La Nina Storm Track Strong EL Nino Storm Track La Nina El Nino Florida Dry Season Slide Courtesy: NWS Melbourne, FL

Normal Ocean Surface Temperatures (°C) January Equator Date Line Equatorial ocean temperatures are normally warmest in the western Pacific and coolest in the eastern Pacific. In the central and eastern Pacific, there is a lot of year-to-year variability. Some years are much warmer and wetter (El Niño) and some years are much cooler and drier (La Niña). Warm, Wet Cool, Dry

10 January Ocean Temperatures ( o C) Comparing Normal to El Niño Temperature Departures Temperatures El Niño Normal El Niño: a periodic warming (every 3-6 years) of the central and eastern equatorial Pacific

Not easy to see effect of El Nino on U.S. in a given weather Map or satellite picture Slide Courtesy: NWS Melbourne, FL

El Nino and La Nina have the greatest impact when they are strong – About 50% time Neutral or Near Normal 8 moderate or higher El Niño's and 9 La Niña's in 60 last years Neutral Range Slide Courtesy: NWS Melbourne, FL

El Niño’s influence on Atlantic hurricane activity is well known El Niño increases the vertical wind shear over the Atlantic, suppressing hurricane activity. More Shear Increased Wind Shear, Fewer Hurricanes Warm, Wet

Global El Niño Impacts El Niño impacts are strongest and most extensive in winter. Some impacts are positive, some are negative

Wintertime Impacts in North America El Niño: Pacific jet stream, storm track are south of normal Polar jet stream well into Canada Fewer arctic outbreaks

16 El Niño is present across the equatorial Pacific Ocean. Ocean surface temperatures (SSTs) are +0.5 o C to +1.5 o C (1 o -3 o F) above-average across the central and eastern equatorial Pacific. El Niño is expected to strengthen and last through the winter. A moderate strength event is most likely. ENSO Alert System Status: El Nino Advisory Current and Expected Conditions The current El Niño began in June. Temperature Departures ( o C): September 2009

Niño Region SST Departures ( o C) Recent Evolution The latest weekly SST departures are: Niño 4 1.4ºC Niño ºC Niño 3 0.8ºC Niño ºC

18 Moderate El Niño Forecast Moderate Event peaking in Nov-Jan

19

Why More Severe Weather? Four key ingredients are typically present at some point during an El Niño winter/spring:Four key ingredients are typically present at some point during an El Niño winter/spring: - Tropical Moisture associated with frontal systems - Instability - Lifting mechanism (cold fronts) - Atmospheric energy/wind shear courtesy of subtropical jet stream El Niño “sets the stage”, not a cause.El Niño “sets the stage”, not a cause.

Winter Storm Track Shifted South

Jet Stream Top 10 La Niñas Top 10 El Niños Jet stream farther south in El Niño winters favors increased Florida storminess with severe weather/tornadoes possible

El Nino pattern translates to increased risk of tornadoes across the Florida Peninsula.

La Nina pattern produces much lower risk for tornadoes across the Florida Peninsula compared with El Nino years.

South Florida Tornado Events compared to ENSO phase

March 27, 2003: Moderate El Niño Liberty City/Brownsville section of Miami One fatality

March 27, 2003 Everglades in Collier County Photo by Paul Wilson/Ochopee Fire Rescue

April 5, 1925: El Niño?? North Dade: 5 deaths

Precipitation Outlook December-February 2009

Temperature Outlook December-February 2009

Caveats Other intra-seasonal atmospheric cycles such as NAO, PNA and MJO can modulate El Niño effects in weak, neutral and even moderate years. Most intra-seasonal cycles are only reliably predictable up to 14 days in advance. Conflicting/overriding signals can disrupt expected atmospheric conditions. Therefore, eventual strength/magnitude of this El Niño matters!

PNA and NAO Variability

North Atlantic Oscillation Negative Positive Periodic Fluctuation of Pressure Patterns over the North Atlantic Ocean – Scale of Weeks – Primary Impact on Winter Temperature Cold Warm Slide Courtesy: NWS Melbourne, FL

Moderate El Nino: Not What We Expected Strong AO+ Pattern South Florida: Warm and Dry in El Niño Year

Madden-Julian Oscillation: A factor in hurricane season...can also a factor in the winter Negative anomalies (green shading) indicate favorable conditions for precipitation. Positive anomalies (brown shading) indicate unfavorable conditions for precipitation. Winter negative anomalies can enhance precipitation in Florida!

Moderate El Niño (6 events) Strong El Niño (4 events) Near normal Above normal

Summary The current El Niño is expected to strengthen and last into spring. A moderate strength event is most likely this winter. Increased likelihood of above average precipitation and below normal temperatures for South Florida during Winter-Spring. Chance of both is 60% for the November-April period. Average dry season precip: 12-15” interior/west to 15-21” east. Average winter temp: 64-66F interior/west to 67-69F east. Main contribution to lower temperatures will likely come by way of increased cloud cover and precipitation with frontal systems, with main effects on lower daily maximum temperatures. Despite lower temperatures, threat of a significant freeze no higher than normal. Arctic/Polar cold air outbreaks not as frequent or common in El Niño, but can still occur (Jan 2003, Jan 1977).

Main Impacts Increased storminess across the southern U.S. enhances the threat of severe weather in South Florida this winter. Emphasis on potential increased tornado threat. Most killer Florida tornado events occur in El Niño years. Public awareness and response is critical.

Public Awareness Many past Florida tornado events occurred at night. Events originate in data sparse areas (Gulf of Mexico), which presents lack of long lead time situational awareness. Special severe weather alerts ahead of significant events.

Sample Severe Weather Outlook...ENHANCED RISK OF TORNADOES ACROSS PORTIONS OF CENTRAL AND SOUTHERN FLORIDA TONIGHT... THE STORM PREDICTION CENTER IS FORECASTING THE DEVELOPMENT OF STRONG TO SEVERE THUNDERSTORMS ACROSS THIS REGION. CONDITIONS WILL BECOME VERY FAVORABLE FOR ISOLATED STRONG AND POSSIBLY LONG-LIVED TORNADOES. THE REGION IS PARTICULARLY VULNERABLE TO STRONG AND DAMAGING TORNADOES DURING THE OVERNIGHT AND EARLY MORNING HOURS THIS TIME OF YEAR. PERSONS IN THIS AREA ARE URGED TO HAVE HEIGHTENED AWARENESS AND REVIEW WEATHER SAFETY RULES. HAVE A PERSONAL SAFETY PLAN FOR YOU AND YOUR FAMILY AND CAREFULLY MONITOR THE LATEST WATCHES AND WARNINGS FROM THE NATIONAL WEATHER SERVICE. THOSE RESIDING IN MOBILE HOMES...RECREATIONAL VEHICLES...AND OTHER TEMPORARY HOUSING WILL BE UNPROTECTED SHOULD A TORNADO STRIKE.

Monitor local media, NWS web site and NOAA All-Hazards Radio weather.gov/southfloridaS.A.M.E. capable All-Hazards Radio

Thank You Contact information: On the Web: weather.gov/southflorida Phone Recording: Administrative: