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Welcome to the South Florida 2010 Summer/Rainy Season Outlook Robert Molleda Warning Coordination Meteorologist NWS Miami/South Florida Forecast Office Robert Molleda Warning Coordination Meteorologist NWS Miami/South Florida Forecast Office

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2009-2010 Dry Season in Review Above to much above normal precipitation almost all of South Florida. Several flood events, most significant of which occurred along SE coast on December 17-18. Above to much above normal precipitation almost all of South Florida. Several flood events, most significant of which occurred along SE coast on December 17-18.

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Dry Season 2009-2010 Rainfall Wettest Areas Relative to Normal: Coastal sections of east coast and west of Lake Okeechobee.

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Rainfall Totals (in) Nov 1, 2009 Apr 30, 2010 11 th wettest2 nd wettest4th wettest9 th wettest

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Rainfall Totals (in) Nov 1, 2009 Apr 30, 2010 11th wettest16 th wettest

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

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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

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What a Difference One Year Makes...

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Four to Five Times More Rain in 2010 vs 2009

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Four to Seven Times More Rain in 2010 vs 2009

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Lake Level

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Ground Water Levels

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Rainy Season 2010 Outlook

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Rainy Season Facts Median start date is around May 20 th. Median end date is around October 17 th. Start date based loosely on time period of at least three consecutives days of 70+ dewpoints, as well as 80 degree water temps. Also need consistent day-to-day thunderstorm pattern to become established. About 70 percent of yearly rainfall occurs during this period. Average wet season precip: 33 to 44 inches. Median start date is around May 20 th. Median end date is around October 17 th. Start date based loosely on time period of at least three consecutives days of 70+ dewpoints, as well as 80 degree water temps. Also need consistent day-to-day thunderstorm pattern to become established. About 70 percent of yearly rainfall occurs during this period. Average wet season precip: 33 to 44 inches.

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Typical Summer Rainfall At least one significant tropical disturbance or tropical cyclone necessary to produce significant summer rainfall over a large area. Otherwise, summer rainfall patterns can vary widely from location to location and even within season. Global scale weather patterns influenced by ENSO (El Nio/La Nia) can play a role in summer rainfall. At least one significant tropical disturbance or tropical cyclone necessary to produce significant summer rainfall over a large area. Otherwise, summer rainfall patterns can vary widely from location to location and even within season. Global scale weather patterns influenced by ENSO (El Nio/La Nia) can play a role in summer rainfall.

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El Nio Going Away Models are split with some keeping ENSO netural and some going to La Nia by late summer/fall. CFS model consensus has La Nia conditions during late summer /fall.

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Weak Summer Signals El Nio on the decline and should dissipate by June or July This means neutral ENSO conditions for much of summer, with possibility of La Nia by late summer/fall. Long-term precipitation signals are weak during neutral ENSO conditions, leading to low confidence in outlook. El Nio on the decline and should dissipate by June or July This means neutral ENSO conditions for much of summer, with possibility of La Nia by late summer/fall. Long-term precipitation signals are weak during neutral ENSO conditions, leading to low confidence in outlook.

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May/June Historical Analogs Northwest winds in mid levels often provide decreased atmospheric moisture but greater instability over South Florida. Looking at years with similar large-scale patterns can help in predicting long-term conditions

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CFS model shows likelihood of drier than normal in May/June Long-term models use current conditions and project out in time.

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July/August Historical Analogs Middle tropospheric winds more normal in historical analogs

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CFS Model: Closer to normal July/August?

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September/October Historical Analogs Historical analogs show near normal with weak corresponding atmospheric signal. Tropical systems can disrupt overall atmospheric pattern.

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CPC outlook May-July Precip

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CPC outlook August-October Precip

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Historical Analogs By Site

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Miami

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West Palm Beach

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Naples

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May-July Temperatures

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August-October Temperatures

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Outlook for Summer/Rainy Season 2010 Climate models indicate transition from El Nio to neutral conditions by June/July, with possibility of weak La Nia conditions by August/September. Due to expected weak signal from global scale indicators like ENSO, confidence is VERY LOW in long term rainfall outlook. Median rainy season start date: May 20/27. Best outlook for 2010 wet season is for near normal precipitation, with equal chances of above or below normal. Climate models indicate transition from El Nio to neutral conditions by June/July, with possibility of weak La Nia conditions by August/September. Due to expected weak signal from global scale indicators like ENSO, confidence is VERY LOW in long term rainfall outlook. Median rainy season start date: May 20/27. Best outlook for 2010 wet season is for near normal precipitation, with equal chances of above or below normal.

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2010 Outlook and Potential Impacts Rainfall largely dependent on organized tropical systems which are impossible to predict well in advance. Warmer than normal temperatures possible, especially if drier scenario verifies. Wet winter lead to higher than normal ground and lake water levels. Threat of localized flooding high, especially during wet periods typically seen in early part of rainy season. Severe weather season usually lasts into July. This means strong thunderstorms with damaging wind gusts, hail, flooding and even tornadoes. Rainfall largely dependent on organized tropical systems which are impossible to predict well in advance. Warmer than normal temperatures possible, especially if drier scenario verifies. Wet winter lead to higher than normal ground and lake water levels. Threat of localized flooding high, especially during wet periods typically seen in early part of rainy season. Severe weather season usually lasts into July. This means strong thunderstorms with damaging wind gusts, hail, flooding and even tornadoes.

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Hurricane Seasonal Forecasts and Assessing Risk From Them

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Seasonal Forecasts Pieces to the Puzzle Sea surface temperatures Rainfall over Africa Pressure patterns over Atlantic Upper-level winds Intra-seasonal changes Sea surface temperatures Rainfall over Africa Pressure patterns over Atlantic Upper-level winds Intra-seasonal changes

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Seasonal Forecasts Good for possible basin-wide trends, but not necessarily for specific locations. Addresses conditions over a very large area and time scale which often are not representative of individual locations. Active season does not automatically imply South Florida hurricane impact. Individual storms motion and intensity dependent on factors that can vary and fluctuate within the season. Good for possible basin-wide trends, but not necessarily for specific locations. Addresses conditions over a very large area and time scale which often are not representative of individual locations. Active season does not automatically imply South Florida hurricane impact. Individual storms motion and intensity dependent on factors that can vary and fluctuate within the season.

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South Florida Hurricane Landfalls Per Year vs ENSO (since 1925) Average Overall Hurricane Frequency: 1 in 4 years 35% difference between El Nio/Neutral and La Nia Frequency

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Hurricane Anniversaries 75 th anniversary of Florida Keys Labor Day Hurricane (1935). Category 5; hundreds dead. 50 th anniversary of Hurricane Donna (1960). Category 4; center passed over Keys and just south of Naples area. Effects felt as far north as Miami. Significant storm surge flooding in Naples/Everglades City. 75 th anniversary of Florida Keys Labor Day Hurricane (1935). Category 5; hundreds dead. 50 th anniversary of Hurricane Donna (1960). Category 4; center passed over Keys and just south of Naples area. Effects felt as far north as Miami. Significant storm surge flooding in Naples/Everglades City.

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Concluding Remarks Time to prepare for hurricane season is NOW. Seasonal forecasts NOT necessarily an indicator of South Florida risk. Tropical storms are dangerous, too. Monitor latest forecasts and warnings via media outlets, NWS web site at weather.gov/southflorida NOAA Weather Radio. It only takes one. weather.gov/southflorida Time to prepare for hurricane season is NOW. Seasonal forecasts NOT necessarily an indicator of South Florida risk. Tropical storms are dangerous, too. Monitor latest forecasts and warnings via media outlets, NWS web site at weather.gov/southflorida NOAA Weather Radio. It only takes one. weather.gov/southflorida