Tropical cyclone forecast model: Difference between revisions

Revision as of 16:17, 13 April 2007

Revision as of 05:37, 6 July 2007

Line 1:

[[Image:NHC_Atlantic_Forecast_Error_Trends.gif|thumb|200px|right|Average trends in forecast errors by the [[National Hurricane Center]]]]

A '''tropical cyclone prediction model''' is a computer program that uses [[meteorology|meteorological]] data to [[weather predictionforecasting|predictforecast]] the motion and intensity of [[tropical cyclone]]s. Such models utilize powerful [[supercomputer]]s with sophisticated [[mathematical model]]ing software and meteorological data to calculate paths and intensities. There are two general types, statistical and dynamical, and two primary types of forecasts, track and intensity.

==Track models==

Line 10:

*'''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.

*'''VICBAR''' and '''LBAR'''

*'''NHCP Aviation''' primarily predictsforecasts wind direction and speed and provides input for other models.

*'''GFDL''' ([[Geophysical Fluid Dynamics Laboratory]]) and an interpolated version, '''GFDI'''

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

Line 16:

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

Beginning in [[2007]], the [[National Centers for Environmental Prediction|NCEP]] Hurricane-WRF will be used to help predictforecast track, intensity, and rainfall from tropical cyclones.<ref>WRF Program Coordinator. [http://wrf-model.org/development/wexob/meetings/Monthly-PC-Report-31Oct04.pdf Monthly Report of the WRF Program Coordinator.] Retrieved on [[2007-04-10]].</ref>

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"/>

Line 22:

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 predictionsforecasts 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 - the source of the [[1-2-3 rule]] - although the errors have been decreasing.

==Intensity models==

Line 28:

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 predictionforecast, 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 predictionforecast.

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

*'''RI Scheme''' (Rapid Intensification) uses output from SHIPS to determine the probability of rapid intensification.

As with track models, intensity models are not perfect. They increase in accuracy as the future time of the predictionforecast approaches the present. That is, a model is more accurate in the short term than in the long term. Intensity models are considered to be inferior to track models in that it is much more difficult to predictforecast intensity changes of a tropical cyclone than it is to predictforecast its course.

==See also==