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{{Short description|Computer program that uses meteorological data to forecast tropical cyclones}}
{{good article}}
[[File:Ernesto2006modelsprdogdogdogmputer]]s with sophisticated [[mathematical model]]ing software and meteorological data to [[numerical weather prediction|calculate future weather conditions]]. [[Statistical model]]s forecast the evolution of a tropical cyclone in a simpler manner, by extrapolating from historical datasets, and thus can be run quickly on platforms such as [[personal computer]]s. Statistical-dynamical models use aspects of both types of forecasting. Four primary types of forecasts exist for tropical cyclones: [[tropical cyclone track forecasting|track]], intensity, [[storm surge]], and [[tropical cyclone rainfall climatology|rainfall]]. Dynamical models were not developed until the 1970s and the 1980s, with earlier efforts focused on the storm surge problem.▼
[[File:Ernesto2006modelspread.png|thumb|upright=1.35|Significant track errors still occur on occasion, as seen in this [[Hurricane Ernesto (2006)|Ernesto (2006)]] early forecast. The [[National Hurricane Center|NHC]] official forecast is light blue, while the storm's actual track is the white line over [[Florida]].]]<!--image stacked below trend-map (same width) -->
▲A '''tropical cyclone forecast model''' is a computer program that uses [[
Track models did not show [[forecast skill]] when compared to statistical models until the 1980s. Statistical-dynamical models were used from the 1970s into the 1990s. Early models use data from previous model runs while late models produce output after the official hurricane forecast has been sent. The use of consensus, ensemble, and superensemble forecasts lowers errors more than any individual forecast model. Both consensus and superensemble forecasts can use the guidance of global and regional models runs to improve the performance more than any of their respective components. Techniques used at the [[Joint Typhoon Warning Center]] indicate that superensemble forecasts are a very powerful tool for track forecasting.▼
▲Track models did not show [[forecast skill]] when compared to statistical models until the 1980s. Statistical-dynamical models were used from the 1970s into the 1990s. Early models use data from previous model runs while late models produce output after the official hurricane forecast has been sent. The use of [[consensus forecast|consensus]], [[ensemble forecasting|ensemble]], and superensemble forecasts lowers errors more than any individual forecast model. Both consensus and superensemble forecasts can use the guidance of global and regional models runs to improve the performance more than any of their respective components. Techniques used at the [[Joint Typhoon Warning Center]] indicate that superensemble forecasts are a very powerful tool for track forecasting.
==Statistical guidance==
[[File:Isabel2003rcliper.jpg|thumb|
The first statistical guidance used by the [[National Hurricane Center]] was the Hurricane Analog Technique (HURRAN), which was available in 1969. It used the newly developed [[HURDAT|North Atlantic tropical cyclone database]] to find storms with similar tracks. It then shifted their tracks through the storm's current path, and used ___location, direction and speed of motion, and the date to find suitable analogs. The method did well with storms south of the [[25th parallel north|25th parallel]] which had not yet turned northward, but poorly with systems near or after recurvature.<ref name="models">{{cite book|pages=288–292|url=https://books.google.com/books?id=6gFiunmKWWAC&pg=PA297
A series of statistical-dynamical models, which used regression equations based upon CLIPER output and the latest output from [[primitive equations|primitive equation]] models run at the National Meteorological Center, then [[National Centers for Environmental Prediction]], were developed between the 1970s and 1990s and were named NHC73, NHC83, NHC90, NHC91, and NHC98.<ref name="NHCmodel"/><ref name="Simpson">{{cite book|url=https://books.google.com/books?id=P7DnIb2XNg0C&
In regards to intensity forecasting, the Statistical Hurricane Intensity Prediction Scheme (SHIPS) utilizes relationships between environmental conditions from the [[Global Forecast System]] (GFS) such as vertical [[wind shear]] and [[sea surface temperature]]s, climatology, and persistence (storm behavior) via multiple regression techniques to come up with an intensity forecast for systems in the northern Atlantic and northeastern Pacific oceans.<ref name="NHCmodel"/>
==Dynamical guidance==
[[File:Sloshrun.gif|thumb|upright=1.3|Example of a SLOSH run]]
{{See also|History of numerical weather prediction}}
The first dynamical hurricane track forecast model, the Sanders Barotropic Tropical Cyclone Track Prediction Model (SANBAR),<ref>{{cite journal|author=R.W. Burpee|name-list-style=amp |year=2008|title=The Sanders Barotropic Tropical Cyclone Track Prediction Model (SANBAR)|journal=Meteorological Monographs|volume=33|issue=55 |pages=233–240|doi=10.1175/0065-9401-33.55.233|doi-access=free|bibcode=2008MetMo..33..233B }}</ref> was introduced in 1970 and was used by the National Hurricane Center as part of its operational track guidance through 1989. It was based on a simplified set of atmospheric dynamical equations (the equivalent barotropic formulation) using a deep layer-mean wind.
During 1972, the first model to forecast storm surge along the [[continental shelf]] of the United States was developed, known as the [[Special Program to List the Amplitude of Surges from Hurricanes]] (SPLASH).<ref>{{cite web|url=http://slosh.nws.noaa.gov/sloshPub/pubs/SLOSH_TR48.pdf|title=SLOSH: Sea, lake, and Overland Surges from Hurricanes. NOAA Technical Report NWS 48|author=Jelesnianski, C. P., J. Chen, and W. A. Shaffer|date=April 1992|accessdate=2011-03-15|publisher=[[National Oceanic and Atmospheric Administration]]|page=2}}</ref> In 1978, the first hurricane-tracking model based on [[Atmospheric dynamics#Dynamic meteorology|atmospheric dynamics]] – the movable fine-mesh (MFM) model – began operating.<ref name="Shuman W&F">{{cite journal|last=Shuman|first=Frederick G.|authorlink=Frederick Gale Shuman|title=History of Numerical Weather Prediction at the National Meteorological Center|journal=[[Weather and Forecasting]]|date=September 1989|volume=4|issue=3|pages=286–296|issn=1520-0434|doi=10.1175/1520-0434(1989)004<0286:HONWPA>2.0.CO;2|bibcode=1989WtFor...4..286S}}</ref> The Quasi-Lagrangian Limited Area (QLM) model is a multi-level primitive equation model using a [[Cartesian coordinate system|Cartesian]] grid and the [[Global Forecast System]] (GFS) for boundary conditions.<ref name="models"/> In the early 1980s, the assimilation of satellite-derived winds from water vapor, infrared, and visible satellite imagery was found to improve tropical cyclones track forecasting.<ref>{{cite journal|url=http://www.bom.gov.au/amm/docs/1996/lemarshall2.pdf|page=275|title=Tropical Cyclone ''Beti'' – an Example of the Benefits of Assimilating Hourly Satellite Wind Data|author1=Le Marshall |author2=J. F. |author3=L. M. Leslie |author4=A. F. Bennett |last-author-amp=yes |journal=Australian Meteorological Magazine|volume=45|year=1996}}</ref> The [[Geophysical Fluid Dynamics Laboratory]] (GFDL) hurricane model was used for research purposes between 1973 and the mid-1980s. Once it was determined that it could show skill in hurricane prediction, a multi-year transition transformed the research model into an operational model which could be used by the [[National Weather Service]] for both track and intensity forecasting in 1995.<ref>{{cite web|url=http://www.gfdl.noaa.gov/operational-hurricane-forecasting|author=[[Geophysical Fluid Dynamics Laboratory]]|title=Operational Hurricane Track and Intensity Forecasting|publisher=[[National Oceanic and Atmospheric Administration]]|date=2011-01-28|accessdate=2011-02-25}}</ref> By 1985, the Sea Lake and Overland Surges from Hurricanes (SLOSH) Model had been developed for use in areas of the [[Gulf of Mexico]] and near the United States' East coast, which was more robust than the SPLASH model.<ref>{{cite journal|author1=Jarvinen B. J. |author2=C. J. Neumann |lastauthoramp=yes |year=1985|title=An evaluation of the SLOSH storm surge model|journal=Bulletin of the American Meteorological Society|volume=66|issue=11 |pages=1408–1411|bibcode=1985BAMS...66.1408.|doi=10.1175/1520-0477-66.11.1408}}</ref>▼
▲During 1972, the first model to forecast storm surge along the [[continental shelf]] of the United States was developed, known as the [[Special Program to List the Amplitude of Surges from Hurricanes]] (SPLASH).<ref>{{cite web|url=http://slosh.nws.noaa.gov/sloshPub/pubs/SLOSH_TR48.pdf|title=SLOSH: Sea, lake, and Overland Surges from Hurricanes. NOAA Technical Report NWS 48|author=Jelesnianski, C. P., J. Chen, and W. A. Shaffer|date=April 1992|
The [[Beta Advection Model]] (BAM) has been used operationally since 1987 using steering winds averaged through the 850 hPa to 200 hPa layer and the Beta effect which causes a storm to drift northwest due to differences in the [[coriolis effect]] across the tropical cyclone.<ref>{{cite web|author=Glossary of Meteorology|date=June 2000|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=beta+effect&submit=Search|title=Beta Effect|publisher=[[American Meteorological Society]]|accessdate=2008-05-05}}</ref> The larger the cyclone, the larger the impact of the beta effect is likely to be.<ref name="NAVY">{{cite web|author=[[United States Navy]]|url=http://www.nrlmry.navy.mil/~chu/chap4/se100.htm|title=Section 1. Influences on Tropical Cyclone Motion|accessdate=2011-02-25|year=2011}}</ref> Starting in 1990, three versions of the BAM were run operationally: the BAM shallow (BAMS) average winds in an 850 hPa to 700 hPa layer, the BAM Medium (BAMM) which uses average winds in an 850 hPa to 400 hPa layer, and the BAM Deep (BAMD) which is the same as the pre-1990 BAM.<ref name="Simpson"/> For a weak hurricane without well-developed central thunderstorm activity, BAMS works well, because weak storms tend to be steered by low-level winds.<ref name="NHCmodel"/> As the storm grows stronger and associated thunderstorm activity near its center gets deeper, BAMM and BAMD become more accurate, as these types of storms are steered more by the winds in the upper-level. If the forecast from the three versions is similar, then the forecaster can conclude that there is minimal uncertainty, but if the versions vary by a great deal, then the forecaster has less confidence in the track predicted due to the greater uncertainty.<ref name="ensbook">{{cite book|url=https://books.google.com/books?id=6RQ3dnjE8lgC&pg=PA261#v=onepage&q&f=false|title=Numerical Weather and Climate Prediction|author=Warner, Thomas Tomkins |publisher=[[Cambridge University Press]]|year=2010|isbn=978-0-521-51389-0|pages=266–275|accessdate=2011-02-11}}</ref> Large differences between model predictions can also indicate wind shear in the atmosphere, which could affect the intensity forecast as well.<ref name="NHCmodel"/>▼
▲The [[Beta Advection Model]] (BAM) has been used operationally since 1987 using steering winds averaged through the 850 hPa to 200 hPa layer and the Beta effect which causes a storm to drift northwest due to differences in the [[coriolis effect]] across the tropical cyclone.<ref>{{cite web|author=Glossary of Meteorology|date=June 2000|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=beta+effect&submit=Search|title=Beta Effect|publisher=[[American Meteorological Society]]|
Tested in 1989 and 1990, The Vic Ooyama Barotropic (VICBAR) model used a [[spline (mathematics)|cubic-B spline]] representation of variables for the objective analysis of observations and solutions to the shallow-water prediction equations on nested domains, with the boundary conditions defined as the global forecast model.<ref>
{{cite journal | doi = 10.1175/1520-0493(1992)120<1628:ANSMFH>2.0.CO;2 | year = 1992 | volume = 120 | pages = 1628–1643 | title = A Nested Spectral Model for Hurricane Track Forecasting | author = Demaria, Mark | journal = Monthly Weather Review | last2 = Aberson | first2 = Sim D. | last3 = Ooyama | first3 = Katsuyuki V. | last4 = Lord | first4 = Stephen J. | issn = 1520-0493 | issue = 8|bibcode = 1992MWRv..120.1628D | doi-access = free }}</ref>
[[File:Irene13.gif|
The [[Hurricane Weather Research and Forecasting model|Hurricane Weather Research and Forecasting]] (HWRF) model is a specialized version of the [[Weather Research and Forecasting model|Weather Research and Forecasting]] (WRF) model and is used to [[weather forecasting|forecast]] the track and [[tropical cyclone scales|intensity]] of [[tropical cyclone]]s. The model was developed by the [[National Oceanic and Atmospheric Administration]] (NOAA), the [[United States Naval Research Laboratory|U.S. Naval Research Laboratory]], the [[University of Rhode Island]], and [[Florida State University]].<ref>{{cite web|publisher=[[University Corporation for Atmospheric Research|UCAR]] press release|url=http://www.ucar.edu/news/releases/2006/wrf.shtml|title=Weather Forecast Accuracy Gets Boost with New Computer Model|
===Timeliness===
Some models do not produce output quickly enough to be used for the forecast cycle immediately after the model starts running (including HWRF, GFDL, and FSSE). Most of the above track models (except CLIPER) require data from [[atmospheric model|global weather models]], such as the GFS, which produce output about four hours after the [[synoptic time]]s of 0000, 0600, 1200, and 1800 Universal Coordinated Time (UTC). For half of their forecasts, the NHC issues forecasts only three hours after that time, so some "early" models
==Consensus methods==
[[File:WRF rita spread2.jpg|thumb|
Using a consensus of forecast models reduces forecast error.<ref name="TBK">{{cite web|author=Kimberlain, Todd|url=http://www.wpc.ncep.noaa.gov/research/TropicalTalk.ppt|title=Tropical cyclone motion and intensity talk|date=June 2007|
In early 2013, The [[NAVGEM]] replaced the NOGAPS as the Navy's primary operational global forecast model. For the 2013 season, and until model verification can occur, it is not being utilized in the development of any consensus forecasts.
For intensity, a combination of the LGEM, interpolated GFDL, interpolated HWRF, and DSHIPS models is known as the ICON consensus. The lagged average of the last two runs of models within the ICON consensus is called the IVCN consensus.<ref name="NHCmodel">{{cite web|url=http://www.nhc.noaa.gov/pdf/model_summary_20090724.pdf|pages=1–7|title=Technical Summary of the National Hurricane Center Track and Intensity Models|date=July 2009|
GFS, the Japanese GSM, the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), the UKMET, the Japanese TYM, the GFDL with NOGAPS boundary conditions, the [[Air Force Weather Agency]] (AFWA) Model, the Australian Tropical Cyclone Local Area Prediction System, and the Weber Barotropic Model.<ref name="STIPS"/>
==Ensemble methods==
{{further|Ensemble forecasting}}
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.<ref>{{cite journal|last=Epstein|first=E.S.|title=Stochastic dynamic prediction|journal=[[Tellus A|Tellus]]|date=December 1969|volume=21|issue=6|pages=739–759|doi=10.1111/j.2153-3490.1969.tb00483.x|bibcode=1969Tell...21..739E}}</ref>
The JMA has produced an 11-member ensemble forecast system for typhoons known as the Typhoon Ensemble Prediction System (TEPS) since February 2008, which is run out to 132 hours into the future. It uses a lower resolution version (with larger grid spacing) of its GSM, with ten perturbed members and one non-perturbed member. The system reduces errors by an average of {{convert|40|km|mi}} five days into the future when compared to its higher resolution GSM.<ref>{{cite web|url=http://www.jma.go.jp/jma/jma-eng/jma-center/rsmc-hp-pub-eg/techrev/text11-2.pdf|title=Outline of the Typhoon Ensemble Prediction System at the Japan Meteorological Agency|author1=Yamaguchi, Munehiko |author2=Takuya Komori |
The Florida State Super Ensemble (FSSE) is produced from a suite of models which then uses statistical regression equations developed over a training phase to reduce their biases, which produces forecasts better than the member models or their mean solution. It uses 11 global models, including five developed at [[Florida State University]], the Unified Model, the GFS, the NOGAPS, the United States Navy NOGAPS, the Australian Bureau of Meteorology Research Centre (BMRC) model, and Canadian [[Recherche en Prévision Numérique]] (RPN) model. It shows significant skill in track, intensity, and rainfall predictions of tropical cyclones.<ref>{{cite book|pages=532–545|url=https://books.google.com/books?id=c-rY28QQCj8C&
The Systematic Approach Forecast Aid (SAFA) was developed by the Joint Typhoon Warning Center to create a selective consensus forecast which removed more erroneous forecasts at a 72‑hour time frame from consideration using the United States Navy NOGAPS model, the GFDL, the Japan Meteorological Agency's global and typhoon models, as well as the UKMET. All the models improved during SAFA's five-year history and removing erroneous forecasts proved difficult to do in operations.<ref>{{cite journal|title=Notes and Correspondence: Operational Evaluation of a Selective Consensus in the Western North Pacific Basin|author=Sampson, Charles R., John A. Knaff, and Edward M. Fukada|pages=671–675|date=June 2007|journal=Weather and Forecasting|volume=22|doi=10.1175/WAF991.1|issue=3|bibcode = 2007WtFor..22..671S |doi-access=free}}</ref>
==Sunspot theory==
A 2010 report correlates low [[sunspot]] activity with high [[cyclone|hurricane]] activity. Analyzing historical data, there was a 25% chance of at least one hurricane striking the continental United States during a peak sunspot year; a 64% chance during a low sunspot year. In June 2010, the hurricanes predictors in the US were not using this information.<ref>{{Cite news | first=Jim | last=Waymer | title=Researchers:Fewer sunspots, more storms
==Hurricane forecast model accuracy==
The accuracy of hurricane forecast models can vary significantly from storm to storm. For some storms the factors affecting the hurricane track are relatively straightforward, and the models are not only accurate but they produce similar forecasts, while for other storms the factors affecting the hurricane track are more complex and different models produce very different forecasts.<ref>{{cite web|url=http://www.hurricanescience.org/science/forecast/models/modelskill/|title=Hurricanes: Science and Society: Hurricane Forecast Model Accuracy|last=[NULL]
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==References==
{{Reflist
==External links==
* [http://www.nrlmry.navy.mil/~chu/chap5/se000.htm Tropical Cyclone Forecasters Reference Guide, Chapter 5] {{Webarchive|url=https://web.archive.org/web/20060711131519/http://www.nrlmry.navy.mil/~chu/chap5/se000.htm |date=11 July 2006 }}
* [http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/ Model Analyses and Forecasts from NCEP] {{Webarchive|url=https://web.archive.org/web/20071223181220/http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/ |date=23 December 2007 }}
* [http://www.nhc.noaa.gov/aboutmodels.shtml National Hurricane Center Forecast Model Background and Information]
{{Atmospheric, Oceanographic and Climate Models}}
▲{{Use dmy dates|date=January 2011}}
{{DEFAULTSORT:Tropical Cyclone Forecast Model}}
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[[Category:Numerical climate and weather models]]
[[fr:Prévision des cyclones tropicaux#Modèles de prévision]]
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