IWTC VI Costa Rica November 2006 Summary Session Jim Davidson

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IWTC VI Costa Rica November 2006 Summary
Session Jim Davidson
Quantitative Forecasts of TC Landfall in
relation to an Effective Warning System
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Effective Warning System
EWS the targetted communication of timely,
relevant, understandable and easily accessible
warnings - prepared using a mix of the best
available model guidance and forecasting
skill. The primary objective of a warning system
is to empower individuals and communities to
respond appropriately to a threat in order to
reduce the risk of death, injury, property loss
and damage. - or simpler still and in fewer
words - Warnings need to engage the people at
risk - and stimulate them to take suitable
protective action.
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Role of the RSMCs/TCWCs
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Established Facts
1. All rapporteurs highlighted the fact that
landfall parameter prediction is highly dependent
on the cyclones track. At a particular location,
even small deviations in track can result in
vastly different impacts from wind, storm tide,
precipitation and flooding. 2. Most deaths in
cyclones continue to be caused by flooding,
landslips and mudslides. 3. With the steady
growth in coastal population and infrastructure,
we are witnessing what amounts to a quantum leap
in vulnerability (and therefore risk) in many
cyclone prone areas, irrespective of trends in
cyclone numbers and intensities. Importantly,
evacuation times have increased accordingly. 4.
Tropical cyclone speed at landfall is also
critical in terms of potential wind damage and
rainfall/flooding. The faster the cyclone is
moving, the lower the risk of wind and flood
damage.
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Landfall Parameters

• WIND both temporal and spatial (over
  varying terrain and topography)
• RAINFALL both temporal and spatial
• FLOODS both riverine and localised
• STORM TIDE (storm
  surge normal tide wave setup)
• WAVES including setup and runup
• The landfall phase is defined as that period
  of a cyclones lifecycle bounded by the immediate
  approach of the cyclone to the coast through to
  the early part of its transition over land.
  Glancing blows (by say destructive winds) is a
  special case.

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Relative Strengths
in the TC landfall forecast process

• Track forecasting (but small deviations do
  matter)
• Storm surge modelling (but dependent on inputs)
• Hydrological modelling (but dependent on inputs)
• NWP (including mesoscale/nested/coupled models)
• Remote sensing data (eg scatterometer, dopplers)
• Dvorak technique (with some reservations)

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Relative Weaknesses
in the TC landfall forecast process

• Forecasting intensity, structure, structural
  change
• Forecasting spatial and temporal rainfall
  patterns
• Modelling wave action (including small islands)
• Modelling riverine flooding storm tide
  waves
• Wind-Pressure relationships (cyclone dependent)
• Forecasting fine scale wind features upon
  landfall
• Forecasting the wind decay rate over land
  (SHIPS)
• Surface upper air obs networks in many areas
• Quality of topographic bathymetric data
• Public understanding of the storm tide threat

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Macau Workshop Priorities
The participants gave the following priority
ranking in regards to improving tropical cyclone
landfall forecasts 1. Further improvements in
track landfall forecasts 2. Improved predictions
of tropical cyclone-related precipitation
following landfall 3. Advances in understanding
and predictions of structure and intensity during
and following landfall, and from tropical storm
stages to extra-tropical transition and 4.
Further applications of storm surge models,
including improved specification of the
meteorological forcing.
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Recommendation Groupings

• ENSEMBLE PREDICTION SYSTEMS (single model?
  probabilities)
• CONSENSUS FORECASTS (multiple-model?
  probabilities)
• PARAMETRIC MODELS (probabilities what if
  scenarios)
• STORM TIDE WAVES and RAINFALL FLOODS
• STRUCTURE WIND PRESSURE
• OTHERS
• Capacity Building, Training, Seminars,
  Workshops, Symposia, Simulator Models (Macau
  Workshop).
• Field Experiments, Demonstration Projects,
  WWRP US Landfall Programs, Australian TCCIP,
  Aircraft Reccies/Aerosonde.
• Observations (eg for forecast verification
  and model calibration)

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Ensemble Prediction Systems
WMO (8) The meeting considers small focus
workshops to be a useful means to organise
research-operational-hydrological interaction on
topics of particular interest to the operational
community. The meeting endorses the increasing
use and application of ensemble prediction
systems (EPS) in forecasting tropical cyclones.
RESEARCH (13) The meeting recommends that the
research community explore the use of ensemble
forecasting techniques for tropical cyclone
forecasting including track, intensity,
Quantitative Precipitation Forecasts (QPF), storm
surge, wind waves and flood forecasting. OPERATIO
NAL (4) It is recognised that ensemble
forecasting techniques may provide an important
opportunity to improve tropical cyclone track
predictions. To be able to utilize these
techniques in an optimum way, it is recommended
that(1) Ensemble-based products be made
available to all RSMCs and Tropical Cyclone
Warning Centres, who should undertake
verification of these techniques, and (2)
Training be provided on how to apply these
techniques in an operating setting.     
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Ensemble Prediction Systems
Storm surge predictions are readily affected by
the error in tropical cyclone predictions in
terms both of their tracks and of intensities.
Taking into account this, ensemble (-like) and
probabilistic methods and outputs should be
considered to use in operational storm surge
forecast. There is a need to continue in
improving operational hydrologic and hydraulic
flood modeling, and this includes consideration
of a tighter coupling with meteorological,
hydrological/hydraulic, and tidal modeling
outputs where useful. We need to have a better
definition of the track and intensity forecast of
tropical cyclone path and quantitative
precipitation forecast (QPF) associated to
tropical models. The use of ensemble forecast and
short term QPF should be considered.
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Consensus Forecasts
OPERATIONAL (2) Consensus forecasting techniques
have been demonstrated to improve track forecasts
provided an adequate number of skillful forecasts
is available. It is recommended that all major
NWP centres make available track and intensity
forecasts, and radius of gale/storm force winds
out to 120 hours or beyond with access via GTS
and controlled access on a suitable website
(e.g., WMO). The WMO should request the European
Centre for Medium-range Weather Forecasts to make
available forecasts of tropical cyclones in their
deterministic model and their tropical ensemble
when it is operational. OPERATIONAL (3)
Consensus forecasts should be closely evaluated
to identify (1) the minimum number and
optimal combination of forecast members that adds
value to the forecast process

(2) scenarios that yield small errors and

(3) strategies to deal with situations when the
consensus forecast does not work (e.g.,
bifurcation scenario when members are in two
different track types)
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Consensus Forecasts
- nil so far -
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Parametric Models
RESEARCH (7) Parametric wind models form a basis
for a range of forecast and diagnostic
applications. Yet many such models are kept
confidential or have not been adequately tested.
The meeting recommends that a public domain
parametric wind field model, fully tested and
verified by peer review, be developed to provide
the standard for comparison purposes. RESEARCH
(15) A parametric model of precipitation
associated with a landfalling storm should be
developed combining
1. A short-range
track and intensity forecast
2. Rainfall rates
derived from satellite and radar imagery
calibrated from a rain gauge network.
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Parametric Models

• More extensive use of parametric wind field
  models in operations is recommended for their
• quality surface wind estimates compared with
  Dvorak
• relatively low cost effort compared with NWP

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Storm TideWaves RainfallFloods
WMO (2) Storm surge and wave height forecasting
is still a significant problem in many tropical
cyclone-affected countries. WMO should endorse
and encourage the establishment of storm surge
techniques and models, including river flooding
and wave action (especially for small islands),
for regions that do not have this capability. In
addition, vulnerability assessments should be
conducted for all countries threatened by storm
surge. RESEARCH (6) While considerable progress
has been made in storm surge forecasting in the
last several years, the meeting recognises that
this capability needs to be improved and extended
to real-time forecasts of lowland inundation.
Thus the meeting recommends that current storm
surge and wave setup models should be improved
via validation using measurements, through
intercomparison studies, and through improvement
of parametric wind models. OPERATIONAL (9) One
of the main impacts of tropical cyclones is the
inundation of coastal areas. To address this
problem, it is recommended that techniques for
forecasting inundation areas be considered and
applied, including the use of inundation maps
with the combined effects of river floods and
storm surge.
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Storm TideWaves
Storm surge predictions are readily affected by
the error in tropical cyclone predictions in
terms both of their tracks and of intensities.
Taking into account this, ensemble (-like) and
probabilistic methods and outputs should be
considered to use in operational storm surge
forecast. As mesoscale NWP models with high
resolution are having ability to solve tropical
cyclone fields, the use of the results of these
NWP models in tropical storm surge modeling
should be investigated. Total storm tide water
level is the combined effect of storm surge, wave
set-up and high tide, and so accurate prediction
of wind waves and tidal height together with
their non-linear interaction with the storm surge
in the model is essential, but prediction methods
for wave setup are not well established yet.
Therefore, further studies of wave setup
prediction method are needed.
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RainfallFloods
There is a need to continue in improving
operational hydrologic and hydraulic flood
modeling, and this includes consideration of a
tighter coupling with meteorological,
hydrological/hydraulic, and tidal modeling
outputs where useful. We need to have a better
definition of the track and intensity forecast of
tropical cyclone path and quantitative
precipitation forecast (QPF) associated to
tropical models. The use of ensemble forecast and
short term QPF should be considered. Some other
works that need to be considered include- (ii)
revision of current rainfall inputs to hydrologic
models to allow for gridded rainfall inputs from
improved operational rainfall spatial analysis
and forecast rainfall grids from NWP models
(iii) digital representation of hydrologic model
sub-areas to enable improved spatial rainfall
inputs (iv) use of radar-rainfall estimation, and
forecasting for short lead times, for flash flood
situations. Intense rainstorms brought about by
tropical cyclones often caused severe landslides
and debris flows, which have claimed many lives
and properties. It is imperative that the flood
forecasting agencies do research into and develop
forecasting models for landslides and debris
flows. Currently this is an area where the USGS
and NWS are partners to develop such forecasting.
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www.bom.gov.au
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Single Day Forecast
Up to 8 global models are combined using the
probability matched ensemble mean technique
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Day 1 to Day 4 Forecast
Up to 8 global models are combined using the
probability matched ensemble mean technique
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Day 5 to Day 8 Forecast
Up to 8 global models are combined using the
probability matched ensemble mean technique
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Probability Forecasts
chance is the proportion of available models
predicting rain at or above the given threshold
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StructureWindPressure
WMO (5) Tropical cyclone intensity should not be
defined solely by a single parameter such as
central pressure or maximum wind. A more detailed
structural analysis is required. The WMO should
encourage forecast centres to report within the
current WMO format structural information such as
quadrant gale radii, eye size, and radius of
outer closed isobar in international exchanges of
both real-time and best track data. In addition,
the time of occurrence and the value of the
minimum pressure, and an indication of the
occurrence of an eye passage should be added to
the synoptic code. This information is needed to
determine the maximum wind-minimum central
pressure relationship associated with tropical
cyclones. RESEARCH (16) The lack of
observational data has caused difficulties with
the calibration of the Dvorak intensity analysis
technique. It is recommended that calibration or
re-calibration of the Dvorak technique, and all
pressure-wind relationships, be undertaken in all
basins. OPERATIONAL (7) There is a need for a
standard conversion chart that enables users to
convert between different wind-averaging periods
and gust factors. The meeting endorses the RSMC
recommendation for updating the conversion chart
in the Global Guide on Tropical Cyclone
Forecasting and requests that the updated values
be distributed to TCWCs as soon as they become
available. In addition, the chart should be
updated on a regular basis as more research into
conversion factors comes to hand.
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Doppler Radar image showing powerful wind
damage streaks in RED ISSUE Difficulty of
applying the Category scale
to the more complex cyclones such as
LARRY
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StructureWindPressure
Contributions to asymmetry in TC structure due to
motion and proximity to land could be comparable.
Interaction between them may be important. Full
investigation is needed. Extreme wind gusts
induced by convective, coherent or vortex-related
features could be damaging at ground level but
not necessarily represented by the broad-brush
destructive potential scales (e.g. Saffir
Simpsons). Better characterization making use of
increased observations (Doppler radar, tower
surface wind measurements, GPS dropsondes) should
become possible. Refined surface roughness
length scheme over land in conjunction with very
fine grid could bring more details of microscale
structure of terrain-induced downdrafts
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Concept of a cyclone FRONT 1 dimensional
measure of Size
LARRY had a relatively narrow FRONT
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Storm Tide Warning Graphical Product
--- a picture is worth a thousand words ---
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IWTC VI Costa Rica November 2006 Summary
Session Jim Davidson
Quantitative Forecasts of TC Landfall in
relation to an Effective Warning System