Improving the Prediction of Inland TC Wind Field

Anantha AiyyerBryce Tyner

North Carolina State University

Organization of this Presentation

• Overview of the problem• Summary/timeline of research plan • Proposed deliverable

• Preliminary work• Cases identification• Data sources

Overview of the problem

Motivation:Inland TC winds pose a major forecast challenge

Key Issue:• Current process of inland wind forecasting is fairly subjective

NHC guidance WFO Forecast (discrete text forecast product) (spatially varying wind field)

There appears to be significant scope to infuse objective measures – especially for wind gust forecasts

• There is a substantial body of scientific literature on near-surface TC wind distribution. e.g.,

Huber, M.M., M. DeMaria, and J. Kaplan, 1996: Evaluation of an Empirical Inland Wind Decay Model for the Landfall of Hurricane Opal. Minutes of the 50th Interdepartmental Conference, Miami, FL, Office of Fed. Coord. for Meteor. Services and Supporting Research, NOAA.

Kaplan, J., and M. DeMaria, 1995: A simple empirical model for predicting the decay of tropical cyclone winds after landfall. J. Appl. Meteor., 34, 2499-2512.

Kepert, J.D., 2001: The dynamics of boundary layer jets within the tropical cyclone core. Part I: Linear theory. J. Atmos. Sci., 58, 2469-2484.

Powell, M.D., P.D. Dodge and M.L. Black, 1991: The landfall of Hurricane Hugo in the Carolinas: Surface wind distribution. Wea. and Forecasting, 6, 379-399.

• However, the main thrust of the published literature is on empirical wind decay distributions for general applications: Guidance, not forecast.

Scope for Science Infusion

Research Plan: Two Track Approach

A. Statistical (climatological): Year 1

• Analysis of past forecasts and comparison with available observations

-will identify systematic bias in inland wind forecasts (if any) -will estimate the bounds on observed wind gusts (within margin of sampling) which will help constrain future forecasts

• Stratify cases on the basis of track, intensity, approach speed, etc. -will help in building statistical models of wind speed probabilities

Research Plan: Two Track Approach

B. Dynamical (ingredients based): Years 1-2

• In-depth analysis of select cases to examine processes associated with downward momentum transport within the TC boundary layer

-shed light on relative importance of boundary layer structure/processes, thermodynamic boundaries, surface roughness characteristics etc.-links with severe weather-TC asymmetries prior and post landfall-Synoptic evolution (e.g., Extratropical transition)

• Close connection with the high resolution numerical modeling efforts (Lackmann/Etherton/Gordon and Parker)

Constraints on Proposed Approach

• Need to closely tie any recommendation from this work to current operational procedure (i.e., links with TPC guidance)

• Should not add to forecaster burden (i.e., as few “new” diagnostics as possible)

• Allow inclusion of high resolution numerical model guidance when available(e.g., Hur-NC: Lackmann/Etherton/Gordon)

Project Deliverable (Years 2/3)

• A framework for wind forecasting that builds on the existing method with enhanced scientific basis.

Potential form:A decision flow chart with objective guidance measures based on research outcomes.

Optimistic:An objective metric for the gust factor that can be computed/displayed within the GFE

Collaborative effortkey areas where we could benefit with close interaction

We’d like to get inputs on:

1. The current decision making approach followed by individual forecasters while making inland wind forecast

-How do you approach a given event?

-What features do you focus on?

-What is your rationale for the gust factor?

-How do you collaborate with other pertinent WFOs in real time?

This will help us understand the subjective extent of the current forecast process and major operational challenges involved

Collaborative effortkey areas where we could benefit with close interaction

We’d like to get inputs on:

2. Areas where you would like us to focus our research and suggestions on the type of tools that would be most useful within the GFE framework

This will help us in sharpening our research focus and making sure that the research outcome can be properly implemented in the existing analysis framework

Collaborative effortkey areas where we could benefit with close interaction

We’d like to get inputs on:

3. Specific cases from past seasons

-Help us identify some of your favorite cases

-Help us check our research progress and keep us honest as we report back periodically

-Reanalyze a case or two once we have made significant progress towards an “improved forecast process”

This will help us test the efficacy of the research

Motivational Case Studies

Bryce Tyner

Hanna (2008)

(Courtesy: NHC)

NHC 3 Day Forecast Track

(Issued 00z 5th September)

NDFD Wind Speed Forecast

(Issued 00z 5th September, Valid 00z 6th September)

NDFD Wind Speed Forecast

(Issued 00z 5th September, Valid 00z 6th September)

NDFD Wind Speed Forecast

(Issued 00z 5th September, Valid 12z 6th September)

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NDFD Wind Gust Forecast

(Issued 00z 5th September, Valid 00z 6th September)

NDFD Wind Gust Forecast

(Issued 00z 5th September, Valid 06z 6th September)

NDFD Wind Gust Forecast

(Issued 00z 5th September, Valid 12z 6th September)

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Observed Wind Gust Maximum

Earl (2010): A Successful ForecastWind Speed (kts)

NDFD Issued 2100 UTC 31st August Valid 0300 UTC 3rd September

HRD Surface Wind Analysis 0430 UTC 3rd September

Storms Affecting NC, 1990-2008

• Storms broken up based on track• 30 Storms Analyzed• Several general tracks found

From Atlantic, parallel to coast, whole storm off the coast

Ana (1991) Danielle (1992)Irene (1999) Ivan (2004)

From Atlantic, parallel to coast, part of storm off the coast, part inland

Arthur (1996) Bonnie (1998)Kyle (2002) Bonnie (2004)Barry (2007) Gabrielle (2007)

From Atlantic, storm makes landfall in NC

Bertha (1996) Fran (1996) Dennis (1999)Floyd (1999) Isabel (2003) Charley (2004)Gaston (2004) Ernesto (2006) Hanna (2008)

Northeast propagation in western NC

Beryl (1994) Frances (2004)Ivan (2004) Jeanne (2004)Fay (2008)

From Gulf, northeast propagation through NC

Allison (1995) Josephine (1996)Danny (1997) Earl (1998)Helene (2000) Allison (2001)Alberto (2006)

Tools for Analysis

• NDFD Forecasts• NARR Reanalysis/RUC Analysis• Sounding Data• ASOS 1 min/5min data• Other suggestions?

Thank You!