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					An Examination of the Tropical System –
Induced Flooding in Central New York and
Northeast Pennsylvania in 2004
Tropical Systems Produced Major
Flooding in Central New York and
Northeast Pennsylvania in 2004


   Remains of “Bonnie” – Flash flooding in
    the western Catskills.
   Remains of “Gaston” – Flash flooding in
    the Finger Lakes and Syracuse area.
   Remains of “Frances” – Flash Flooding in
    south central NY.
   Remains of “Ivan” – Major Flooding in
    southern New York and northeast Pa.
Outline
   A brief review of previous research on enhanced
    precipitation in the northeast associated with
    tropical storms transitioning to extra-tropical.
   A brief overview of each storm, including the large-
    scale flow and precipitation pattern associated with
    each storm, as well as each storm’s effects on
    central NY / northeast Pa.
   A little more on two of these storms, with emphasis
    on findings from previous research.
   Summary.
Heavy rain is especially enhanced when enhanced low-level inflow
interacts with coastal fronts and/or terrain.
Topographical map of the New York, Pennsylvania and
Western New England.
Tropical Storm Bonnie

   Tropical storm Bonnie moved north
    across the Gulf of Mexico to northern
    Florida on August 12.
   Moisture “associated with” Bonnie
    produced significant flash flooding in
    the western Catskill mountains and
    northeast Pocono mountains on the
    12th.
Surface plot August 12, 2004 20 UTC.
GFS 00-hr 300 mb hts and wind speed August 12, 18 UTC.
August 12, 2004 16 UTC
August 12, 2004 20 UTC.
Radar estimated rainfall through 00 UTC August 13.
Tropical Storm Gaston

   Tropical Storm Gaston moved north across
    the southern Atlantic, making landfall in
    South Carolina on the 29th.
   The storm weakened to a depression, then
    re-strengthened to a tropical storm as it
    moved north off the Delmarva peninsula on
    the 30th.
   Significant flash flooding occurred on the
    30th in the Finger Lakes and Syracuse area.
Surface plot August 30, 2004 21 UTC.
00-hr GFS 300 mb heights and wind speed August 30, 18 UTC.
August 30, 2004 12 UTC.
August 30, 2004 20 UTC.
Radar estimated rainfall through 00 UTC August 31st.
Hurricane Frances
   The remains of Hurricane Frances moved
    north from the Gulf of Mexico up the west
    slopes of the Appalachians on the 8th.
   The surface low pressure center tracked
    from southwest Pennsylvania north to
    western New York during the morning on
    the 9th.
   Flooding in central New York was confined
    to the central southern tier (much more
    farther west and south).
Surface plot September 9, 2004 12 UTC.
GFS 00-hr 300 mb heights and vorticity September 9, 06 UTC.
September 9, 2004 04 UTC.
September 9, 2004 08 UTC.
Radar estimated rainfall through 2049 UTC, September 9.
Hurricane Ivan

   The remains of Hurricane Ivan moved
    northeast from the central Gulf Coast,
    reaching northern Virginia early on the
    18th.
   Widespread 4 to 7 inch rainfalls over
    northern Pennsylvania and southern
    New York brought major flooding to a
    wide area.
Surface plot September 18, 2004 06 UTC.
GFS 00-hr 300 mb heights and wind speed September 18, 00 UTC.
September 17, 2004 21 UTC.
September 18, 2004 03 UTC.
Radar estimated storm total precipitation through September
18, 2004 18 UTC.
CSTAR research on precipitation and
tropical cyclones in New England
indicates precipitation is maximized
when…

      Upper-level anticyclonic outflow results in an enhanced
       upper-level jet northwest-northeast of the surface cyclone.
      The right entrance region of the upper-level jet is located
       over the potential heavy rain area.
      Enhanced low-level jet develops along with enhanced θe
       advection.
      Precipitation is frequently enhanced by interactions
       between the low-level jet and coastal fronts / topography.
Factors Favorable For Warm Season /
Convective Flash Flooding


       Strong low-level jet (>30 (20) kts) / θe advection.
       Weak mid-level winds / weak mid-level shear.
       Deep warm cloud layer (greater than 3 km).
       Moderate – high “skinny” CAPE south of the heavy
        rain (NCAPE < 0.10).
       Precipitable Water > 130 percent of normal.
       Weak short-wave trof upstream of heavy rain.
       Upper-level divergence / jet entrance region.
In our 4 cases, there
appeared to be two distinct
types…
   Heavy convective rains developing well
    to the north of the tropical cyclone
    (Bonnie and Gaston).
   Heavy rains more directly associated
    with the transitioning tropical cyclone
    (Frances and Ivan).
   Let’s look at a representative case
    from each type in a little more detail.
Tropical Storm Gaston

   Representative of the cases where
    flash flooding developed associated
    with convection well to the north of
    the primary surface low.
           Surface front

6-hr Eta forecast vertical circulation, divergence and wind
speed (shaded) valid 18 UTC August 30st.
        flooding


Eta 6-hr forecast vertical circulation, frontogenesis and negative
EPV (shaded blue) valid August 30, 18 UTC.
Eta 6-hr 925 mb theta-e advection and wind August 30, 18 UTC.
Eta 6-hr lifted index and 3-6 km bulk shear August 30, 18 UTC.
Eta 9-hr BUFKIT sounding at ELM valid August 30, 21 UTC.
     20 kt low-level jet




Eta BUFKIT Time-section of wind at IPT
       Gaston - Summary
   Pronounced upper-level jet entrance region
    coupled with a low-level front.
   Moderate, surface-based instability.
   Weak low-level Өe advection (20 kt low-level jet),
    separate from flow associated with Gaston.
   Mid-level shear (3-6 km) around 10 kts.
   Warm cloud depth around 3 km.
   Precipitable water around 1.6 inches.
   Heaviest rain in the hilly terrain of northern
    Oneida county southwest to the southern edge of
    the Syracuse area.
Ivan

   Representative of the cases with more
    widespread heavy rain associated
    more directly with a tropical cyclone.
   The worst flooding in our county
    warning area since 1996.
         Deep frontal zone




Eta 6-hr vertical circulation, divergence and wind speed
September 18, 06 UTC.
                     flooding


Eta 6-hr vertical circulation, frontogenesis and negative EPV
September 18, 06 UTC.
Eta 6-hr 850 mb theta-e advection and wind September 18, 06 UTC.
Eta 6-hr lifted index and 3-6 km bulk shear September 18, 06 UTC.
Eta 6-hr BUFKIT sounding at IPT valid September 18, 06 UTC.
  Low-level jet




Eta BUFKIT time section of wind speed at IPT
Eta BUFKIT elevated CAPE at IPT
Summary - Ivan
   Pronounced upper-level jet entrance area coupled
    with a low-level front.
   Deep, sloping area of frontogenesis.
   Instability mainly located at mid-levels around 700
    mb.
   Strong low-level Өe advection (40 kt low-level jet).
   Strong instability gradient – mid-level (3-6 km)
    shear 10 to 20 kts.
   Warm cloud depth around 4 km.
   Precipitable water around 1.9 inches.
   Heaviest rain in northern Pennsylvania – no
    obvious, strong topographic influence.
Summary

   Two distinct patterns were identified
    that were associated with flooding.
   Both types had much in common, and
    much in common with other flood
    events studied previously.

				
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posted:8/2/2010
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