An Overview of Features that Enhance Precipitation Associated with Tropical Cyclones

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An Overview of Features that Enhance
Precipitation Associated with Tropical Cyclones
Meredith Croke Dr. Lian Xie, Dr. Michael Kaplan,
Dr. Gary Lackmann and Kermit Keeter
CSTAR Meeting August 2, 2006
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Outline

• Motivation, Objective Methodology
• Brief Precipitation Analysis
• Climatological StudyPotential Forecasting
  Techniques
• Planetary Scale Analysis (gt10,000 km)
• 72-hours prior to landfall through landfall
• Synoptic Scale Analysis (2000-10,000 km)
• 36-hours prior to landfall through landfall
• Meso-alpha (200-2000 km) Scale Analysis
• 18-hours prior to landfall through landfall
• Recent Case Study (T.S. Alberto)
• Conclusions Ideas for Future work

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Motivation

• North Carolina is a prime target for recurving
  Atlantic TCs.
• Forecasting precipitation totals is complicated
  by the interactions with midlatitude systems.
• Goal Improve collaborated QPF between NWS RAH
  and the SERFC that are used to predict river
  flood water levels.

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Objectives

• Determine features that creates an environment
  conducive to an enhanced rain event.
• Differentiate between heavy and light
  precipitation during landfalling TCs.
• Create a conceptual model for forecasters to use
  from 72-hours prior to landfall through landfall.
  
• Begins with Planetary analysis ? downscale to
  meso-alpha scale features.

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Methodology

• Three part study examines both intrinsic and
  extrinsic features.
• 28 TCs that made landfall or tracked along
  coastal North Carolina since 1953 ? 2 groups
  formed for climatological analysis based on 3-day
  daily mean precipitation.
• Heavy gt 15 mm
• Light lt 15 mm
• Synoptic and Mesoscale analyses using 12 TCs.

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Composite Precipitation and Storm Tracks
Heavy
Light
Track Difference is NOT statistically significant.
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Landfall Tropical Cyclone Intensity
Tropical Cyclone intensity (neither maximum or
landfall) is Not a dominate factor in
precipitation.
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Translation Speed
Translation speed is not a dominate factor in
precipitation Over North Carolina.
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Planetary Analysis
NCEP/NCAR
72-hours Prior to Landfall 250 hPa Geopotential
Heights
Heavy
Light
Neg. Tilted Trough

-
Weaker Anomalies
Stronger Anomalies
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Planetary Analysis
NCEP/NCAR
At Landfall 250 hPa Geopotential Heights
Heavy
Light
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PV Analysis
24-hours Prior to Landfall
Heavy
Light
High PV
250-500 mb Composite layer Potential Vorticity
(PVU)

• PV ?conserved for adiabatic, frictionless motion
  directly relates dynamics diabatic heating.
• PV ?examine interactions between TCs and
  upper-tropospheric troughs instead of more
  traditional variables such as vorticity, height
  and wind

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PV Analysis
12-hours Prior to Landfall
Heavy
Light
Pos. Tilted PV Max
Neg. Tilted PV Max
250-500 mb Composite layer Potential Vorticity
(PVU)
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PV Analysis
At Landfall
Heavy
Light
Pos. Tilted PV Max
Neg. Tilted PV Max
250-500 mb Composite layer Potential Vorticity
(PVU)
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Moisture Flux Analysis
48-hours Prior to Landfall
Heavy
Light
850-925 mb Composite layer Moisture Flux
(gmkg-1s-1), moisture flux vectors (gmkg-1s-1)
and moisture flux convergence (gkg-1s-1)
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Moisture Flux Analysis
24-hours Prior to Landfall
Heavy
Light
850-925 mb Composite layer Moisture Flux
(gmkg-1s-1), moisture flux vectors (gmkg-1s-1)
and moisture flux convergence (gkg-1s-1)
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Moisture Flux Analysis
At Landfall
Heavy
Light
850-925 mb Composite layer Moisture Flux
(gmkg-1s-1), moisture flux vectors (gmkg-1s-1)
and moisture flux convergence (gkg-1s-1)
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Surface Features

• Surface ridge of high pressure extends southward
  into inland North Carolina ? weak cold air
  damming event.
• Surface ridge strengthens, shift in wind
  direction ? strengthens coastal front.
• Frontogenesis used to look for a coastal front ?
  leads to enhanced precipitation west of front.
• Frontogenesis can be a major contributor to an
  intense rain event.

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Frontogenesis, Temperature, Wind MSLP
18-hours Prior to Landfall
Light
Heavy
MSLP (mb contours) 1000 mb Isotherms (oC color
fill), and wind barbs (ms-1)
1000 mb Temperature (oC), Frontogenesis (oC
100km-1 3hr-1) Winds (ms-1)
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Frontogenesis, Temperature, Wind MSLP
At Landfall
Light
Heavy
MSLP (mb contours) 1000 mb Isotherms (oC color
fill), and wind barbs (ms-1)
1000 mb Temperature (oC), Frontogenesis (oC
100km-1 3hr-1) Winds (ms-1)
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Forecasting SchematicHeavy Events
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A Recent Event

• T. S. Alberto
• Landfall on June 13, 2006 over Northern Florida
• Tracked northeast through North Carolina.
• Note Track location outside the domain study,
  but similarities existed.
• All slides courtesy of NWS Gail Hartfield

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Upper trough configuration Alberto
Positively tilted trough
Upper divergence max
12z Tue 6/13 NAM run
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PV configuration Alberto
High PV to the northwest, negatively tilted
configuration
This PV can increase upper divergence
12z Tue 6/13 NAM run
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Low level moisture flux Alberto
High moisture flux convergence into NC
Very high moisture transport into NC image
arrows
12z Tue 6/13 NAM run
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Near-surface frontogenesis, temperatures, MSLP,
wind Alberto
Weak damming signature
Strong frontogenesis
12z Tue 6/13 NAM run
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Tropical Storm Alberto, June 2006
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Conclusions

• TC intrinsic features ? not primary mechanism
  that determine precipitation during landfalling
  TC over North Carolina.
• Connection between longer period planetary scale
  features and shorter duration mesoscale features
  ? interact to create an enhanced rain event.

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Conclusions

• The presence of the following features creates an
  environment favorable for enhanced precipitation
• Negatively tilted upper trough over Southern
  Plains.
• Strong upper-level divergence inland of TC
• Strong inland moisture flux beginning prior to
  landfall.
• A wedge of cool air, surface high pressure over
  Northeast? signals of cold air damming.
• Formation of coastal front along Carolinas
  coastline.

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Possible Future Work

• Examine significant features in depth
• Can strength of CAD be determined?
• Upper-level trough, pos. or neg. tilt?
• Storm total precipitation vs. 3-day
  precipitation.
• Include all storms that tracked a specific
  distance inland along the Southeast and Gulf
  Coasts.
• Use modern storms that can be examined using
  higher resolution NARR data.
• In depth modeling analysis of a few storms (T.S.
  Alberto) that were heavy rain events.
• Examine 2 storms with similar intensities,
  tracks, etc. but different precipitation totals.

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Acknowledgements

• Dr. Xie, Dr. Kaplan, and Dr. Lackmann
• Kermit Keeter and the entire NWS
• COMET CSTAR
• All of you for coming and allowing me to speak
  about Tropical Cyclones even though Im in
  Spokane, WA!

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QUESTIONS???
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and Eastern North Carolina was never the same
after that