nwp for tropical cyclone forecasting · july 2017 upgrade – slight improvement (res same) model...
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Text• NWP upgrades
• Track forecasting
– Consensus
– Ensembles
NWP for Tropical Cyclone forecasting
Rewa, 1993/94http://www.bom.gov.au/cyclone/history/rewa.shtml
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Models : ECMWF•https://software.ecmwf.int/wiki/display/FCST/Implementation+of+IFS+cycle+43r3
Deterministic 9km resolution; twice per day, 137 levels to 10 days Ensemble forecast (EPS): twice per day 51 members 18 km
91 levels to 15 days aheadMon/Thurs 00UTC extended to 1 month ahead (Monthly Forecast 18/36km)
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Model upgrades : ECMWF•https://software.ecmwf.int/wiki/display/FCST/Implementation+of+IFS+cycle+43r3
July 2017 upgrade – slight improvement (res same)
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Model upgrades : GFS
Skill similar to ECMWFGlobal model run at ~13km resolution to +240hAvailability of GFS ensembles? 21 membersRecent upgrades not indicating much improvement for TCsWidespread availability from different sites e.g. https://ruc.noaa.gov/tracks/
http://www.nco.ncep.noaa.gov/pmb/changes/
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Model upgrades : UK
Skill near to EC and GFS since major 2014 upgradeJuly 2017 upgrade: Deterministic: 17km (TBC if now lower) Ensembles: 36 members at 20km resolution (previously 24 at 33km) Available on SWFDDP site: http://swfddp.metservice.com/global-ukmo-pacific-tc-data/tc-tracks
http://www.metoffice.gov.uk/research/modelling-systems/unified-model/weather-forecasting
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Model: HWRF
http://www.emc.ncep.noaa.gov/gc_wmb/vxt/HWRF/index.php
nested within GFS with variable resolution – higher for core 8/6/2km – yes 2km for inner core! Run for all systems globally can run 7 TCs at once inc. lowsIntensity results encouraging. 2017 Upgrade: ongoing improvement in track and intensity though likely NH (ocean coupling) is better than SH
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Model upgrades : HWRF
http://www.emc.ncep.noaa.gov/gc_wmb/vxt/HWRF/index.php
Blanca 20153km run
2km run, more symmetric and smaller sized storm
Courtesy: V. Tallapragada, NCEP
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Aust/Regional 12km
TropicalCyclone 12km
CityBased 5km
ACCESS NWP
ACCESS-G Global (~25km)ACCESS-TC variable domain 12km resolution for TCModule trackinghttp://www.bom.gov.au/australia/charts/viewer/index.shtml
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9/30Models : the othersJMA, COAMPS, GFDN/L, NAVGEM
and others
JMA: ~20km resolution; trailing other globals in Aust regionCOAMPS: Experimental CTCX 5km resolution
Nested in NAVGEMGFDL: nested in GFS – Skill here?GFDN: GFDL version nested in NAVGEM
NAVGEM: US Navy Global model still has some skill but trails
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10/30Verification: Track JTWC2016 in WPAC (update)
[typical for all basins]
Consensus beat JTWC at all forecast timesMeso-models, except HWRF, continue to lag global models (GFS/EC/UK)GFS/EC/UK performed similarly, except at Day 5 where GFS had ~50nm larger errors
Courtesy: JTWC
JTWCCONGFSUKECHWRF
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Track Forecasting –The Australian Consensus approach
How to choose what goes in? NRL approach to test a model: compare result if you take
the model out from the consensus. Does it add value?
Standard members – nine modelsEC + GFS + HWRF + UK + ACCESS-TC (Tier 1)+ COAMPS(TX) + JMA + GFDL/GFDN* + NAVGEM (Tier 2)For tropical lows greater selective approaches;Using previous runs of EC/GFS/HWRF/UK case by case basis;Occasional erratic behaviour by GFDN and COAMPS;GFS/JMA ensemble mean used by JTWC
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The BoM Consensus approachNon-SELECTIVE (NCON) – robust most of time
TC Christine: Model position check
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The BoM Consensus approachNon-SELECTIVE (NCON) – robust most of time
TC Christine: spread in shifted models Tier 1 models consistentcf climatology (grey)cf previous forecast (dashed)
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Input to Forecast Track Map
TC Christine: Uncertainty and gales shape watch/warning areas
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The BoM Consensus approachSELECTIVE (SCON)
Will Quang hit Exmouth??
COAMPS (green) +UK/GFDL(to east)others inc. EC/GFS/A-TC further west; JMA (light green) further westQuestion: Should we 1. discard COAMPS as the outlier?
OR2. Just take the consensus of all?
Or 3. …?
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The BoM Consensus approachSELECTIVE (SCON)
Will Quang hit Exmouth??
WEST or EAST?
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The BoM Consensus approachSELECTIVE (SCON)
Will Quang hit Exmouth??
UK last three runs for consistency
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Track Forecasting –The BoM Consensus approach
SELECTIVE (SCON)
Quang: bias to UK (to east)sfc wind comparison at +66hUK stronger being steered by deeper NW'ly flow than other models
JMA also weak – outlier to be discarded?
UKAC
GFSEC
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The BoM Consensus approachSELECTIVE (SCON)
When to be selective: High spread, can explain model behaviourpre-Olwyn: bias to EC and UKUncertainty bulge for other scenarios
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Track Forecasting –The BoM Consensus approach
SELECTIVE (SCON)
Ex-TC Lam: high spread in models – EC Vs GFS/UK !
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Track Forecasting –The BoM Consensus approach
SELECTIVE (SCON)
Track map: high uncertainty – watch Qld and NT side of Gulf but EC treated as 'unlikely'
Note: when being selective ensure reasoning is documented
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Track Forecasting – BEWAREDon't ever be complacent
Sometimes nature doesn't go by the NWP rules
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Track Forecasting – BEWAREDon't ever be complacent
Changes in track close to coast – timing consequences for landfall storm tide e.g. Dylan, Marcia, Yasi…Trochoidal motion
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Track Forecasting - ensembles
EC strike probability – TC Ita
EC ensemble large spreadassist with uncertainty area Esp. "bifurcation" cases
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Applying ensembles
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Applying ensembles
Bright&Nutter 2004Extracting best ensemble member will not
yield the best forecast over time!
attempting to choose or eliminate members may degrade the future value of the ensemble because "bad" members may appear as the best member at a later time.
mmm…
But Quang – can we eliminate some members west or east?
Maybe …
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ADVANCED Track Forecasting - ensembles
Filtering, clustering and super-ensembles
Filter on position/intensityCluster techniques
Useful SOMETIMESBang for buck?
Super-ensembles coming…availability
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ADVANCED: Deterministic Vs Ensemble meanBlack line - determistic
Why is the black line different from the highest probability?
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ADVANCED Track Forecasting
Bifurcation TC Willy
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Track map examples
Courtesy: Elliott&Yamaguchi, IWTC VIII http://www.wmo.int/pages/prog/arep/wwrp/new/documents/Topic1_AdvancesinForecastingMotion.pdf
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Fiji Track map examples:uncertainty and threat areas
Courtesy: Fiji Met Service
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Summary
Forecasting - it is all getting easier!
Questions?
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ExercisesWhat is the probability of impact at
locations A, B and C?
A B
C
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Exercises: EC ensemble
What is the probability of impact at locations A, B and C?
AC
B
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ExercisesWhat is the probability of impact at
locations A, B and C?
AB
C
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ensemble
What is the probability of impact at locations A, B and C? A
CB
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Exercises
How would you go about determining the risk to southern Andhra Pradesh?
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ExercisesHow to use this spread?
Is there a risk to southern Andhra Pradesh?
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ExercisesReal-time: steering pattern in the Pacific
For …Determine the steering pattern based on the 700 and 500hPa winds/heights from HWRF and GFS
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Model upgrades : ACCESS
ACCESS-G upgrade to APS-2 for 2015/16 season resolution 25km from 40km- Possible concern that model may 'overheat' development.
ACCESS-TC variable domain at 12km resolution
New supercomputer will herald opportunities for upgrades in 2016 & 2017
http://www.bom.gov.au/australia/charts/viewer/
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Applying ensembles: should we bother being selective?
US Dewpoint example: different colours represent different ensemble members closest to the analysis (most accurate)
Little spatial correlation between membersNo one member dominates a large regionRed: 1-5 Yellow 6-10 Blue 11-15