1. 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

2. 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.

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

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

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

7. 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

8. 8

9. 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

10. What a Difference One Year Makes...

11. Four to Five Times More Rain in 2010 vs 2009

12. Four to Seven Times More Rain in 2010 vs 2009

13. Lake Level

14. Ground Water Levels

15. Rainy Season 2010 Outlook

16. 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.

17. 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 Niño/La Niña) 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 Niño/La Niña) can play a role in summer rainfall.

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

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

20. 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

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

22. July/August Historical Analogs Middle tropospheric winds more “normal” in historical analogs

23. CFS Model: Closer to normal July/August?

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

26. CPC outlook May-July Precip

27. CPC outlook August-October Precip

28. Historical Analogs By Site

29. Miami

30. West Palm Beach

31. Naples

32. May-July Temperatures

33. August-October Temperatures

34. Outlook for Summer/Rainy Season 2010 Climate models indicate transition from El Niño to neutral conditions by June/July, with possibility of weak La Niña 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 Niño to neutral conditions by June/July, with possibility of weak La Niña 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.

35. 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.

36. Hurricane Seasonal Forecasts and Assessing Risk From Them

37. 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

39. 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.

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

41. 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.

42. 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