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NHC Track and Intensity Models


Updated 19 December 2017

The term "forecast model" refers to any objective tool used to generate a prediction of a future event, such as the state of the atmosphere. The National Hurricane Center (NHC) uses many models as guidance in the preparation of official track and intensity forecasts. The most commonly used models at NHC are summarized in the tables below.

Forecast models vary tremendously in structure and complexity. They can be simple enough to run in a few seconds on an ordinary computer, or complex enough to require a number of hours on a supercomputer. Dynamical models, also known as numerical models, are the most complex and use high-speed computers to solve the physical equations of motion governing the atmosphere. Statistical models, in contrast, do not explicitly consider the physics of the atmosphere but instead are based on historical relationships between storm behavior and storm-specific details such as location and date. Statistical-dynamical models blend both dynamical and statistical techniques by making a forecast based on established historical relationships between storm behavior and atmospheric variables provided by dynamical models. Trajectory models move a tropical cyclone (TC) along based on the prevailing flow obtained from a separate dynamical model. Finally, ensemble or consensus models are created by combining the forecasts from a collection of other models.

Table 1. Summary of global and regional dynamical models for track, intensity, and wind radii.

ATCF ID Global/Regional
Model Name
Horizontal
Resolution
Vertical Levels
and Coordinates
Data
Assimilation
Convective Scheme Cycle/Run Frequency NHC Forecast
Paramter(s)
NVGM/NVGI Navy Global Environmental Model Spectral (~31km) 60 Hybrid Sigma-pressure NAVDAS-AR 4D-VAR Simplified Arakawa Schubert 6 hr (144 hr)
00/06/12/18 UTC
Track and intensity
AVNO/AVNI
GFSO/GFSI
Global Forecast System Spectral (~13km) 64 Hybrid Sigma-pressure GSI/4D-VA EnKF hybrid Simplified Arakawa Schubert 6 hr (180 hr)
00/06/12/18 UTC
Track and intensity
*EMX/EMXI/EMX2 European Centre for Medium-Range Weather Forecasts Spectral (~9km) 137 Hybrid Sigma-pressure 4D-VAR Tiedke mass flux 12 hr (240 hr)
00/12 UTC
Track and intensity
EGRR/EGRI/EGR2 U.K. Met Office Global Model Grid point (~10 km) 70 Hybrid Sigma-pressure 4D-VAR Ensemble Hybrid UKMET 12 hr (144 hr)
00/12 UTC
Track and intensity
CMC/CMCI Canadian Deterministic Prediction System Grid point (~25 km) 80 Hybrid Sigma-pressure 4D-VAR Ensemble Hybrid Kain-Fritsch 12 hr (240 hr)
00/12 UTC
Track and intensity
HWRF/HWFI Hurricane Weather Research and Forecast system Nested Grid point (18-6-2km) 61 Hybrid Sigma-pressure 4D-VAR Hybrid GDAS GFS IC/BC Simplified Arakawa Schubert + GFS shallow convection (6 and 18km) 2km nest - none 6 hr (126 hr)
00/06/12/18 UTC
Runs on request from NHC/JTWC
Track and intensity
CTCX/CTCI NRL COAMPS-TC w/ GFS initial and boundary conditions Nested Grid point (45-15-5 km) 42 Hybrid Sigma-pressure 3D-VAR (NAVDAS) EnKF DART Kain-Fritsch 6 hr (126 hr)
00/06/12/18 UTC
Runs commence on 1st NHC/JTWC advisory
Track and intensity
HMON/HMNI Hurricane Multi-scale Ocean-coupled Non-hydrostatic model Nested Grid point (18-6-2km) 42 Hybrid Sigma-pressure GFS IC/BC Simplified Arakawa Schubert + GFS shallow convection (6 and 18km) 2km nest - none 6 hr (126 hr)
00/06/12/18 UTC
Runs on request from NHC/JTWC
Track and intensity

* Public Access to these models is restricted due to agreements with the data provider.



Table 2. Summary of ensembles and consensus aids for track and intensity.

ATCF ID Model Name or Type Horizontal Resolution Vertical Levels
and Coordinates
Data
Assimilation
Pertubation or Consensus Methods Cycle/Run Frequency Ensemble Members NHC Forecast
Paramter(s)
AEMN/AEMI Global Ensemble Forecast System ~35 km for 1st 192 hr
~52 km for 192-384 hr
64 Hybrid Sigma-pressure GSI/4D-VAR EnKF hybrid 20 of 80 6 hr DA system hybrid EnKF members per cycle 6 hr (384 hr)
00/06/12/18 UTC
20 Track
*UEMN/UEMI U.K. Met Office MOGREPS ~20 km 70 Hybrid Sigma-pressure 4D-VAR EnKF hybrid 44 member EnKF 12 hr (168 hr)
00/12 UTC
11 Track
*EEMN/EMN2 ECMWF EPS ~18 km 91 Hybrid Sigma-pressure 4D-VAR Leading singluar vectors based initial pertubations 12 hr (360 hr)
00/12 UTC
50 Track
*FSSE Florida State Super Ensemble Corrected consensus 6 hr (120 hr)
00/06/12/18 UTC
Track and Intensity
*HCCA HFIP Corrected Consensus Approach Corrected consensus 6 hr (120 hr)
00/06/12/18 UTC
AEMI AVNI CTCI DSHP EGRI EMN2 EMXI HWFI LGEM Track and Intensity
*GFEX 2 model consensus Simple consensus 6 hr (120 hr)
00/06/12/18 UTC
AVNI EMXI Track
TVCN
(Atlantic) (TVCA)
Variable consensus Simple consensus, minimum 2 members 6 hr (120 hr)
00/06/12/18 UTC
AVNI EMXI HWFI CTCI EGRI Track
TVCN
(E. Pacific) (TVCE)
Variable consensus Simple consensus, minimum 2 members 6 hr (120 hr)
00/06/12/18 UTC
AVNI EMXI HWFI CTCI EGRI NVGI Track
TVCX Variable consensus Simple consensus, minimum 2 members, double-weighted EMXI 6 hr (120 hr)
00/06/12/18 UTC
AVNI EMXI HWFI CTCI EGRI Track
RVCN Wind Radii Consensus Multi-model wind radii, bias corrected initial wind 6 hr (120 hr)
00/06/12/18 UTC
AVNI EMXI HWFI 34-kt wind radii
IVCN Intensity variable consensus Simple consensus, minimum 2 members 6 hr (120 hr)
00/06/12/18 UTC
HWFI CTCI DSHP LGEM Intensity

* Public Access to these models is restricted due to agreements with the data provider.



Table 3. Summary of statistical models for track, intensity, and wind radii.

ATCF ID Model Name or Type Comments Prediction Methodology Cycle/Run Frequency NHC Forecast
Paramter(s)
CLP5 (OCD5) CLIPER5 Climatology and Persistence Used to measure skill in a set of track forecasts Multiple regression technique. Inputs are current and past TC motion (previous 12-24hr), forward motion, date, latitude/longitude, and initial intensity 6 hr (120 hr)
00/06/12/18 UTC
Track
SHF5/DSF5 (OCD5) Decay-SHIFOR5 Statistical Hurricane Intensity Forecast Used to measure skill in a set of intensity forecasts, includes land decay rate component Multiple regression technique using climatology and persistence predictors 6 hr (120 hr)
00/06/12/18 UTC
Intensity
TCLP Trajectory-CLIPER Used to measure skill in a set of track or intensity forecasts Substitute for CLIPER and SHIFOR; similar predictors but uses trajectories based on reanalysis fields instead of linear regression 6 hr (168 hr)
00/06/12/18 UTC
Track and intensity
DRCL Wind Radii CLIPER Statistical parametric vortex model Employs climatology with the paramaters determined from 13 coefficients and persistence to produce 34-kt, 50-kt, 64-kt wind radii estimates 6 hr (168 hr)
00/06/12/18 UTC
Wind radii
SHIP Statistical Hurricane Intensity Prediction Scheme Statistical-dynamical model based on standard multiple regression techniques Climatology, persistence, environmental atmosphere parameters, and an ocean component 6 hr (168 hr)
00/06/12/18 UTC
Intensity
DSHP Decay-Statistical Hurricane Intensity Prediction Scheme Statistical-dynamical model based on standard multiple regression techniques Climatology, persistence, environmental atmosphere parameters, oceanic input, and an inland decay component 6 hr (168 hr)
00/06/12/18 UTC
Intensity
LGEM Logistic Growth Equation Model Statistical intensity model based on a simplified dynamical prediction framework A subset of SHIPS predictors, ocean heat content, and variability of the environment used to determine growth rate maximum wind coefficient 6 hr (168 hr)
00/06/12/18 UTC
Intensity

Early versus Late Models

Numerous objective forecast aids (guidance models) are available to help the NHC Hurricane Specialists in the preparation of their official track and intensity forecasts. Guidance models are characterized as either early or late, depending on whether or not they are available to the Hurricane Specialist during the forecast cycle. For example, consider the 1200 UTC (12Z) forecast cycle, which begins with the 12Z synoptic time and ends with the release of the official forecast at 15Z. The 12Z run of the NWS/Global Forecast System (GFS) model is not complete and available to the forecaster until about 16Z, or about an hour after the forecast is released – thus the 12Z GFS would be considered a late model since it could not be used to prepare the 12Z official forecast.

Multi-layer dynamical models are generally, if not always, late models. Fortunately, a technique can be used to take the latest available run of a late model and adjust its forecast to apply to the current synoptic time and initial conditions. In the example above, forecast data for hours 6-126 from the previous (06Z) run of the GFS would be adjusted, or shifted, so that the 6-h forecast (valid at 12Z) would exactly match the observed 12Z position and intensity of the tropical cyclone. The adjustment process creates an "early" version of the GFS model for the 12Z forecast cycle that is based on the most current available guidance. The adjusted versions of the late models are known, for historical reasons, as interpolated models.

Interpreting Forecast Models

NHC provides detailed information on the verification of its past forecasts with a yearly verification report (http://www.nhc.noaa.gov/verification/verify3.shtml). On average, NHC official forecasts usually have smaller errors than any of the individual models. An NHC forecast reflects consideration of all available model guidance as well as forecaster experience. Therefore, users should consult the official forecast products issued by NHC and local National Weather Service Forecast Offices rather than simply look at output from the forecast models themselves. Users should also be aware that uncertainty exists in every forecast, and proper interpretation of the NHC forecast must incorporate this uncertainty. NHC forecasters typically discuss forecast uncertainty in the Tropical Cyclone Discussion (TCD) product. NHC also prepares probabilistic forecasts that incorporate forecast uncertainty information (http://www.nhc.noaa.gov/aboutnhcprobs.shtml).

NOAA/NWS Models

The National Weather Service produces some of the models used by the National Hurricane Center. These models are run by NOAA/NWS National Centers for Environmental Prediction (NCEP) Central Operations (NCO). Output images from the NOAA/NWS models can be found through NCEP's Model Analyses and Guidance (MAG) interface. Raw data from the models can be found through the NOAA Operational Model Archive and Distribution System (NOMADS).

Other model background information

Read about the Inland Wind Model and the Maximum Envelope Of Winds