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