Tropical cyclone forecast model: Difference between revisions

Revision as of 20:34, 21 May 2006

Revision as of 05:36, 23 May 2006

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==Track models==

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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 Guidence 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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*'''UKMET''' ([[United Kingdom]] [[Meteorological Office]])

*'''NOGAPS''' ([[United States Navy]] Global Atmospheric Prediction System)

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

AllSome 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, LBAR, and GFDILBAR - are run using a 12-hour-old forecast for the current time. "Late" models, whichsuch as the GFS and GFDL, finish after the advisory has already been issued,. These models are interpolated[[interpolation|interpolatef]] to the current storm position for use in the nextfollowing advisoryforecast 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.

Like all weather forecasts, track predictions are more accurate in the short term than in the long term. Average errors for the [[United States]] [[National Hurricane Center]] are around 100, 200, and 300 [[nautical miles]] in 1, 2, and 3 days, respectively. This is- the source of the [[1-2-3 rule]] - although the errors have been decreasing.

==Intensity models==

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This is a list of intensity models, some of which have additional notes.

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.