Tropical cyclone forecast model
4142447
210439999
2008-05-05T23:02:09Z
Thegreatdr
825275
/* Track models */
[[Image:NHC Atlantic Forecast Error Trends.gif|thumb|200px|right|Average trends in forecast errors by the [[National Hurricane Center]]]]
A '''tropical cyclone forecast model''' is a computer program that uses [[meteorology|meteorological]] data to [[weather forecasting|forecast]] 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==
[[Image:Ernesto2006modelspread.png|thumb|right|250 px|Significant errors in track still occur on occasion, as seen in one of [[Hurricane Ernesto (2006)|Ernesto's (2006)]] early forecasts. The [[National Hurricane Center]]'s official forecast is in light blue.]]
{{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 Guidance 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 vertically-averaged winds and computes trajectories provided by the GFS model to provide track forecasts. There are three forms, BAMD (BAM Deep, 850-200 hPa), BAMM (BAM Medium, 850-400 hPa) and BAMS (BAM Shallow, 850-700 hPa) that use different altitudes of wind.
*'''VICBAR'''
*'''LBAR''' (Limited area sine transform BARotropic) is a two-dimensional track prediction model.
*'''NHCP Aviation''' primarily forecasts wind direction and speed and provides input for other models.
*'''GFDL''' ([[Geophysical Fluid Dynamics Laboratory]]) is a limited-area baroclinic model developed specifically for hurricane prediction. It is run four times a day (six hours apart).
*'''UKMET''' ([[United Kingdom]] [[Meteorological Office]])
*'''NOGAPS''' ([[United States Navy]] Global Atmospheric Prediction System)
*'''A98E''' is a statistical-dynamical prediction model using geopotential heights from the GFS forecast to modify the CLIPER forecast. It incorporates portions of the NHC90 and NHC98 Atlantic forecast models.
*'''GFS''' ([[National Weather Service]] [[Global Forecast System]]) is the main meteorological model for the United States. The model is run four times a day (six hours apart). It is a merger and expansion of the AVN and MRF models and is extended out to 384 hours.
*'''HWRF''' [[Hurricane Weather Research and Forecasting model|Hurricane-WRF]] is a dynamical nested model that uses the NAM as a source of its background data. HWRF is intended to eventually replace the GFDL as the main nested model for hurricane prediction, but also aides in the forecasting of track, intensity, and rainfall from tropical cyclones. .<ref>[http://www.noaanews.noaa.gov/stories2007/s2885.htm NOAA News Online (Story 2885)<!-- Bot generated title -->]</ref><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> The HWRF was introduced at the beginning of the 2007 hurricane season.
*'''FSSE''' [[Florida State Superensemble]] is a model first used operationally in the 2005 hurricane season and has shown to verify well in tropical cyclone track forecasting. Not a large amount is known about this model as the model is owned by a private company which charges for access to the data.
===Timeliness===
Some models do not produce output quickly enough to be used for the forecast cycle immediately after the model starts running (e.g. HWRF, GFDL, FSSE.) Most of the above track models (except CLIPER) require data from global weather models, such as the GFS, which produce output about four hours after [[synoptic time]]. However, for half of their forecasts, 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 completely accurate. The use of the ensemble method of forecasting, whether it be a multi-model ensemble, or numerous ensemble members based on the global model, helps define the uncertainty and further limit errors. The forecast models are used as a tool that an experienced forecaster will use to assemble an official track forecast.
Like all weather forecasts, track forecasts 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 {{convert|300|nmi|km}} in 1, 2, and 3 days, respectively - the source of the [[1-2-3 rule]] - although the errors have been decreasing.
==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 forecast, similar to CLIPER and CLIPER5 above. Until recently, this was the most consistently accurate.<ref name="2005_Verification"/>
*'''SHIPS''' (Statistical Hurricane Intensity Prediction Scheme) is a statistical model that uses climatological, persistence and synoptic predictors.
***'''RI Scheme''' (Rapid Intensification) uses output from SHIPS to determine the probability of rapid intensification.
*'''DSHP''' (Decay SHIP) is identical to the SHIPS model; however, if the cyclone is forecast to cross land, the intensity will be reduced accordingly.
*'''GFDL''' and '''HWRF''' provide intensity forecasts along with their track forecasts.
*'''FSSE''' provides intensity output in relation to its storm forecast, though varies from other models in taking into account the [[National Hurricane Center]]'s forecasts in addition to standard data sources.
As with track models, intensity models are not perfect. They increase in accuracy the closer you get to the present. In other words, a forecast model are normally 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 forecast intensity changes of a tropical cyclone than it is to forecast its course. Also, errors in the potential course of a tropical cyclone, especially regarding landfall timing, can compound the intensity error.
==See also==
{{tcportal}}
*[[Numerical weather prediction]]
*[[Tropical cyclone]]
*[[Tropical cyclone forecasting]]
*[[Tropical cyclone rainfall forecasting]]
*[[Weather forecasting]]
==References==
{{reflist}}
==External links==
* [http://www.nrlmry.navy.mil/~chu/chap5/se000.htm Tropical Cyclone Forecasters Reference Guide, Chapter 5]
* [http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/ Model Analyses and Forecasts from NCEP]
[[Category:Tropical cyclone meteorology]]
[[Category:Numerical climate and weather models]]
[[fr:Prévision des cyclones tropicaux]]
[[pt:Modelo de previsão de ciclones tropicais]]
[[simple:Tropical cyclone forecast model]]