Tropical Cyclone Consensus
Forecasting Methods Used on Guam
Chip Guard
Warning Coordination Meteorologist WFO Guam
International Training Workshop on Tropic
Cyclone Disaster Reduction
Guangzhou, China
26-31 March 2007
NOAA’s National Weather Service
Consensus
Forecasting Methods
• What is Consensus Forecasting?
– Consensus forecasting is the process of combining different
types or sources of information into a solution that is
hopefully better than any of the parts.
• What is Tropical Cyclone Consensus Forecasting?
– Tropical Cyclone consensus forecasting is the process of
taking multiple sources of predictions and combining them
into a track or intensity forecast that is better than any of the
individual predictions (over a reasonable period of time, e.g.,
a season). This process can be automated.
NOAA’s National Weather Service
Consensus
Forecasting Methods
• Methods of Consensus Forecasting?
– A consensus approach has been used by forecasters and forecast
centers for decades—since the time when multiple forecast options
became available to the centers.
– In the 1990’s, the Joint Typhoon Warning Center began to automate
the consensus process using several different methods:
• Interpolation of model tracks
• Single and multi-model methods
• Weighted and non-weighted
• Selective and non-selective
• Position consensus vs. vector motion consensus
(See Andrew Burton’s Paper from IWTC-VI)
NOAA’s National Weather Service
Consensus
Forecasting Methods
• What Consensus Techniques do we use on Guam?
– Our primary forecasts come from the Joint Typhoon Warning
Center (JTWC), now located in Hawaii
– Their track forecasts use the NOGAPS model to produce
numerous ensemble forecasts from which their official forecast
is derived
– Ensembles forecasts are themselves consensus forecasts
– We look at predictions from other forecast centers—many of
these also derived from ensemble forecasts—and evaluate their
performance with and deviations from the JTWC predictions
– Usually our consensus is the forecast of the Joint Typhoon
Warning Center……….but, how can we improve on that?
NOAA’s National Weather Service
Consensus
Forecasting Methods
• We evaluate the initial information
– Are the tropical cyclone fixes good? Can the spread be
explained?
– Are the Dvorak intensity estimates good? Can the spread be
explained?
– Is the initial motion vector good? We have found this to be the
single most important reason why early model forecasts (first
24h) are wrong
– We look at all the data—especially the satellite data—to reassess
the initialization/input data
– We evaluate the NOGAPS model against our National Weather
Service models at the lower, middle and upper levels to assess
similarities and differences
NOAA’s National Weather Service
Consensus
Forecasting Methods
• We evaluate geography and climatology
– Will there be local effects on the track? On the intensity? On
the wind distribution and asymmetry? On the hazards?
– What should we expect from climatology? Does the forecast
exceed the bounds of climatology? If so, is there a physical
explanation for this?
• We Default to Radar Data When the Storm is Near
– We carefully track the radar motion for short and long term
trends
– We use the Doppler to refine and validate storm intensity
– We feed our assessments back to JTWC
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Trochoidal Motion
• USER BEWARE!
• Short term
variations may
not be indicative
of changes in
overall motion of
the tropical
cyclone
Consensus
Forecasting Methods
• We evaluate the lower, middle and upper levels
– Low-levels—analyze Quick SCAT data over our entire area and evaluate
other satellite data, especially visual data if available; sunrise surprise
• High resolution winds (8-min average, 25 km resolution); there is a tendency
to under-estimate winds from data; concept of the minimum maximum
• Reveals size of storm—important for
– gales and storm-force winds; reflects pressure gradients
– storm surge and coverage of damage
– Beta effect on movement speed and down-stream development
• Mid-levels—look for steering levels
• 400-500 hPa for deep storms
• 700-500 hPa for shallower storms (not common)
• 850 hPa for sheared storms
NOAA’s National Weather Service
Consensus
Forecasting Methods
• We evaluate the lower, middle and upper levels
– Upper-levels—analyze 200 hPa level and satellite data
• Analysis is at both the synoptic and meso scales
• This level is important for intensity forecasts
• Identify features and determine how well the models reflect
those features; (e.g., cyclonic cells in the Tropical Upper
Tropospheric Trough (TUTT) or outflow channels)
• Assess shear and meso-scale interactions
– We use microwave data to assess the vertical
structure of the tropical cyclone
NOAA’s National Weather Service
Consensus
Forecasting Methods
• Weighting techniques in track forecasting
– Heavily weight the first 6-12 hours toward persistence
• Thus, initial motion vector is VERY important
– Heavily weight the overall forecast on JTWC. Why?
• They do a good job as do most of the centers
• We can easily discuss the forecasts with them and provide input and data
• If we do change the JTWC forecast, it is as a last resort and only in the first
24 hours
– We used to weight longer range forecasts toward climatology, but it is
getting very difficult to beat the dynamic models for track forecasts
– Look for bifurcations; convey the alternatives to your Emergency Mgr;
timing of the turns can be critical
– We also use the models (out to 7 days) to assess genesis potential; we
combine this knowledge with the MJO predictions and ENSO status
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Consensus
Forecasting Methods
• Weighting techniques in intensity forecasting
– Look for areas of shear
– Look for meso-scale interactions
• Favorable for rapid intensification
– TUTT cell 10-12º from cyclone center
– TUTT cell center NNW of cyclone center
– Multiple outflow channels
• Unfavorable
– TUTT cell within 8° of cyclone center
– Single outflow channel
– Kinks in outflow
– Assess output from intensity forecast models
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Consensus
Forecasting Methods
• Hints for Success in preventing disasters
– Go with persistence in the short term
– Don’t assume; pick up the phone and make sure
– Be proactive; pick up the phone first and make sure
– Go after data; don’t wait for it to come to you
– Develop good satellite interpretation skills; there is up to 36
hours of predictive value in satellite imagery
– It is better to over-forecast than to under-forecast
– Anticipate what could go wrong; communicate concerns or
options with the Emergency Manager
NOAA’s National Weather Service
Consensus
Forecasting Methods
• Hints for Success in Preventing Disasters
– Use the triad of partners: Met/Hydro Services, Emergency
Managers, Media; the public doesn’t care who messed up, they
just know the Government messed up; perception is reality
– No one should know more about the storm than you do
– Know the geography, climatology, risks and vulnerabilities: It’s
free knowledge
– Keep products and information simple; you are talking to
customers, not meteorologists
– Forecast within your capabilities and expertise
– Develop an in-house forecast strategy for every storm or event
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Questions
Our
Anatahan
Volcano
NOAA’s National Weather Service
Volcano Hazards for Guam
GuamGuam
Palau
Anatahan
Palau
Anatahan
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Volcano Hazards for Guam
NOAA’s National Weather Service
Volcano Hazards for Guam
Pagan
Anatahan
NOAA’s National Weather Service
Volcano Hazards for Guam
Pagan Island from Space Shuttle
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Volcano Hazards for Guam
Hawaii
Anatahan
NOAA’s National Weather Service
Volcano Hazards for Guam
Anatahan
Anatahan
NOAA’s National Weather Service
Volcano Hazards for Guam
NOAA’s National Weather Service
Volcano Hazards for Guam
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Volcano Hazards for Guam
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Submarine eruptions
Volcano Hazards for Guam
Ahyi
NW Rota 1
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Volcano Hazards for Guam
New Britain,PNG
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Volcano Hazards for Guam
Rabaul, PNG
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Volcano Hazards for Guam
Pinatubo, Philippines
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Volcano Hazards for Guam
Galunggung, Indonesia
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Volcano Hazards for Guam
Ruang, Indonesia
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Volcano Hazards for Guam
Reventador, Ecuador (not a hazard for Guam)
NOAA’s National Weather Service
Prognosis for Anatahan Eruption
At
Present
• Lava extrusion and small explosions inside the E crater,
and discontinuous low level ash eruption
• Hazards limited to island and to local aviation
•“Open conduit “ for now, but situation can change quickly
• Larger explosive eruption(s) accompanied by large
eruptive column and pyroclastic flows
Possible
Unlikely
• Ash cloud hazards more widespread and severe; small
chance of local tsunami from pyroclastic flows entering the
sea or from flank landslides into sea
• Very large explosive eruption w/ caldera formation (e.g.
Pinatubo), &/or large landslide (e.g. Mount St. Helens)
• Major threat to aviation in case of explosive eruption
• Tsunami generation, Marianas-wide effects
Volcanic Ash – threat to Guam
Volcanoes in the Mariana Islands could produce volcanic
ash on Guam.
Wet ash conducts electricity; can cause short circuits.
Weight of ash (especially wet) can cause roof collapse.
Ash can clog ventilation and drainage systems.
Ash causes wear on moving parts of machinery.
Ash makes roads slippery.
Ash is a serious hazard to aviation
Ash can cause respiratory problems.
Volcanic Haze (VOG)– can affect Guam
Concentration of gases over Guam is usually very low
The haze/dust can cause breathing difficulties for some
people; they should stay indoors
Haze can cause acid rain; Guam is largely calcium
carbonate, which would neutralize the acid.
Haze can obscure mountains and reduce visability.
Not a serious corrosion hazard to aviation.
VOG – The good & bad news
Prevailing winds tend to transport vog and ash toward the west
and southwest, away from Guam; NNE wind bad for Guam.
Topographic traps for vog are not significant in Guam.
Trade
Winds
Geology of Guam is dominated by carbonate, which will
neutralize acid rain.