Tropical cyclone forecast model: Difference between revisions

Revision as of 12:14, 16 January 2007

Revision as of 23:52, 20 February 2007

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==Track models==

{{Expand-section|date=January 2007}}

Some of the track models used by the National Hurricane Center follows: <ref name="Sim_Aberson_FAQ">[http://www.aoml.noaa.gov/hrd/tcfaq/F2.html NHC Tropical Cyclone FAQ Subject F2]</ref> <ref name="NHCsummary_DeMaria">[http://www.nhc.noaa.gov/modelsummary.shtml Summary of the NHC/TPC Tropical Cyclone Track and Intensity GuidenceGuidance Models]</ref> <ref name="2005_Verification">[http://www.nhc.noaa.gov/verification/pdfs/Verification_2005.pdf 2005 NHC Forecast Verification Report]</ref>

*'''CLIPER''' (CLImatology and PERsistence) is a 3-day statistical model ('''CLIPER5''' is a 5-day version of the same model). It uses the current path of a tropical cyclone and an average of historical paths of similar cyclones to come up with a track, and is considered a "no-skill" model. Curiously, until the late 1980s, this was actually the most accurate model. Forecast skill is determined by comparing forecasts against this model. <ref name="2005_Verification"/>

*'''NHC90''' and '''NHC98'''

*'''BAM''' ([[Beta effect|Beta]] and [[Advection]]) uses horizontal winds. There are three forms, BAMD (BAM Deep), BAMM (BAM Medium) and BAMS (BAM Shallow) that use different altitudes of wind.

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*'''GFS''' ([[National Weather Service]] [[Global Forecast System]])

Some models do not produce output quickly enough to be used for the forecast cycle immediately after the model starts running. Most of the above track models (except CLIPER) require data from global weather models, which produce output about four hours after [[synoptic time]]. However, the NHC issues forecasts only three hours after that time, so some "early" models - NHC90, BAM, and LBAR - are run using a 12-hour-old forecast for the current time. "Late" models, such as the GFS and GFDL, finish after the advisory has already been issued. These models are [[interpolation|interpolated]] to the current storm position for use in the following forecast cycle - for example, GFDI. <ref name="NHCsummary_DeMaria"/> <ref name="2005_Verification"/>

No model is ever perfectly accurate because it is impossible to learn exactly everything about the atmosphere in a timely enough manner, and atmospheric measurements that are taken are not always totally accurate. Thus, the models are used as a tool that an experienced forecaster will use to assemble an official track forecast.

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==Intensity models==

{{Expand-section|date=January 2007}}

Some of the intensity models used by the National Hurricane Center follows:<ref name="Sim_Aberson_FAQ"/> <ref name="2005_Verification"/>

*'''SHIFOR''' (Statistical Hurricane Intensity FORecast) and '''SHIFOR5''' uses the average of past storms with similar behaviour as well as an extrapolation of recent behaviour by a storm to arrive at a prediction, similar to CLIPER and CLIPER5 above. Until recently, this was the most consistently accurate. <ref name="2005_Verification"/>

*'''SHIPS''' (Statistical Hurricane Intensity Prediction Scheme) uses current conditions and past storms to arrive at a prediction.

*'''GFDL''' is the same model used in track prediction.