GFDL - Geophysical Fluid Dynamics Laboratory

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2012 GFDL Hurricane Model Ensemble

Ensemble Overview

An ensemble forecast system based on the operational GFDL hurricane model has been developed as part of the regional modeling effort for the Hurricane Forecast Improvement Program (HFIP).

(Figure 1: Ensemble forecast of storm track and intensity)

Figure 1: Ensemble forecast of storm track and intensity

  • Goal: Design and run a simple ensemble based on the operational GFDL model to provide additional real-time guidance on track and intensity.
  • Method: Run at same resolution as the operational GFDL model [parent domain and 2 nests with 1/2° (~55 km), 1/6° (~18 km), and 1/12° (~9 km) horizontal grid spacing, respectively]. Apply perturbations by either modifying the vortex structure, moisture fields, or sea-surface temperatures (SSTs) in the core region.
  • Resources: All forecasts run on NOAA's Jet machine at Earth System Research Laboratory (ESRL) in Boulder, CO.
  • Model configuration:
      Initialization: GFDL Synthetic Bogus Vortex
      Initial and Boundary Conditions: Half of the 16 ensemble members are based on forecasts from NCEP's Global Forecast System (GFS), while the other half use mean fields from NCEP's Global Ensemble Forecast System (GEFS).
      Planetary Boundary Layer (PBL): GFS Non-Local PBL
      Vertical Levels: 42 sigma levels; ~5 levels of relatively high resolution in the PBL; Model top at 10 mb
      Ocean coupling: Princeton Ocean Model (POM); SST fields from the GFS analysis

2012 Ensemble Membership

GP** members represent ATCF output from GFDL's (internal) vortex tracker, while GT** represents HFIP community (external) vortex tracker output.

The global model used for initial and boundary conditions is noted in brackets.

ATCF IDDescription
GP00/GT00Control forecast (same model as NCEP 2012 operational GFDL) [GFS deterministic]
GP01/GT01Unbogussed forecast using the 2012 control model [GFS deterministic]
GP02/GT02Increase NHC-observed Vmax 10%, 34-kt radii 25%, 50-kt radii 40%, ROCI 25% [GFS deterministic]
GP03/GT03Decrease NHC-observed Vmax 10%, 34-kt radii 25%, 50-kt radii 40%, ROCI 25% [GFS deterministic]
GP04/GT04Modification to increase inner-core moisture by a max of 10% [GFS deterministic]
GP05/GT05Modification to decrease inner-core moisture by a max of 10% [GFS deterministic]
GP06/GT06Increase SSTs by a max of 1°C within the initial extent of the TC [GFS deterministic]
GP07/GT07Decrease SSTs by a max of 2°C within the initial extent of the TC [GFS deterministic]
GP08/GT08Control forecast for the NCEP ensemble-based members [NCEP GEFS mean]
GP09/GT09Unbogussed forecast using the 2012 control model [NCEP GEFS mean]
GP10/GT10Increase NHC-observed Vmax 10%, 34-kt radii 25%, 50-kt radii 40%, ROCI 25% [NCEP GEFS mean]
GP11/GT11Decrease NHC-observed Vmax 10%, 34-kt radii 25%, 50-kt radii 40%, ROCI 25% [NCEP GEFS mean]
GP12/GT12Modification to increase inner-core moisture by a max of 10% [NCEP GEFS mean]
GP13/GT13Modification to decrease inner-core moisture by a max of 10% [NCEP GEFS mean]
GP14/GT14Increase SSTs by a max of 1°C within the initial extent of the TC [NCEP GEFS mean]
GP15/GT15Decrease SSTs by a max of 2°C within the initial extent of the TC [NCEP GEFS mean]
GPMN/GTMNEnsemble mean of member numbers 01→15 computed at each lead time where the member availability is at least 6 (40% threshold)

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Products Guide

Typically, for the first (i.e., "primary") storm of a particular forecast cycle, products are available on the website around t+7 hrs. Products from any second and third storm arrive at the website at t+8 and t+9 hrs, respectively.


QUICK VIEW

A series of products displayed on one page to provide the user with a quick view of the selected storm's forecasted track, intensity, size, and cyclone phase space.

Track and intensity

Produced from either the ATCF-styled text output from the HFIP community tracker or GFDL internal tracker.

"HFIP community (external) tracker" vs. "GFDL (internal) tracker": For the track and intensity products, two versions of the same product are provided (viewed by clicking each version's tab). One version uses data from the external vortex tracker, while the other version uses data from the internal vortex tracker. The "HFIP community (external) tracker" runs after the forecast is completed and processes the model's 6-hourly grib output to produce ATCF-styled text files, which are used by many of our graphical products. Storm track is generally better represented by the external tracker because the algorithm tracks multiple vortex parameters rather than just minimum sea-level pressure (as with the internal tracker). The "GFDL (internal) tracker" runs with the forecast model and is able to produce track and intensity output at every hour. Additionally, 6-hourly intensity data are smoothed over a 3-hr window.

Track: Track positions of all 16 members and the ensemble mean are plotted every 6 hrs (and labeled every 12 hrs). Track data from the model's two vortex trackers are provided. Note: output from these trackers are prone to having significant differences in storm location (and therefore, intensity) when the storm is weak (<TS) and/or makes landfall. As previously discussed, vortex tracking in the HFIP external tracker is more robust than in the GFDL internal tracker (i.e., multiple vortex parameters are tracked, rather than just minimum sea-level pressure). However, data are only available every 6 hrs for the external tracker, while for the internal tracker, track and intensity data are available every hour.

Track ellipses: The colored ellipses indicate the region that two-thirds of the ensemble member tracks occupy at a given lead time. This can be interpreted as the region the tropical cyclone will be in with 66.67% confidence based on that particular ensemble forecast. The ellipses are a simple way to highlight the directions of greatest variance [e.g., across-track and along-track (speed)] in the ensemble forecast positions. The ensemble mean ("GPMN" or "GTMN") is shown in red and is plotted every 6 hours. Ensemble track positions (shown as asterisks) and ellipses are color-coded for days 0, 1, 2, 3, 4, and 5.

Intensity (Max sfc wind): [Top panel] Box plot time series of maximum surface wind every 6 hrs. The number of members present (out of 16) at each 24-hr interval is shown in parentheses, which is provided to indicate if any member dissipates the storm before the 126-hr forecast is completed. [Bottom panel] Spaghetti plots showing each member's maximum surface wind every 6 hrs. The percentage of dissipated members is shown in parentheses at each 24-hr interval.

Hourly max sfc wind: [Top panel] Box plot time series of maximum surface wind at 1-hr intervals. These data are produced by the GFDL internal tracker. However, unlike the "GP**" ATCF data, the hourly intensity data are not smoothed over time (i.e., the hourly data represent instantaneous values of maximum surface wind). The number of members present (out of 16) at each 12-hr interval is shown in parentheses, which is provided to indicate if any member dissipates the storm before the 126-hr forecast is completed. [Bottom panel] Spaghetti plots showing each member's maximum surface wind at 1-hr intervals. The percentage of dissipated members is shown in parentheses at each 12-hr interval.

Intensity (Max sfc wind and min SLP): [Top panel] Exactly the same as the box plots for "Intensity (Max sfc wind)". [Bottom panel] Box plot time series of minimum sea-level pressure every 6 hrs. This is shown with max sfc wind to illustrate their evolution together over time.

Combined track and intensity: Ensemble view of storm tracks, color-coded to also show storm intensity (max sfc wind). Tracks and intensities from the HFIP community tracker are plotted every 6 hrs (starting at hour 0), while the GFDL internal tracker has data plotted at every hour (starting at hour 1). As discussed before, track plots from these two vortex trackers are prone to having significant differences in storm location when the storm is weak (<TS) and/or makes landfall.

Min sea-level pressure: As in the "Intensity (Max sfc wind)" product, but for minimum sea-level pressure.

Max wind swaths and probabilities

Produced from GFDL wind swath generator text output.

Max wind speed probabilities: These products show the probability of 34- (tropical storm force), 50-, and 64-kt (hurricane force) 10-m winds occurring in the ensemble. The probabilities are calculated using the maximum wind speed swaths from the 16 ensemble members. The National Hurricane Center (NHC) observed initial location of the storm is indicated by the blue star. The color bar matches what is used in the official NHC wind speed probabilities graphics.

Max wind speed swaths: Swaths of maximum 10-m winds for each ensemble member over the duration of the forecast period (max 126 hrs). Each member's wind swath can be viewed by moving the cursor over each tab. Storm track is plotted every hour starting at hour 1. The color bar highlights each cyclone intensity category.

Cyclone phase space

Produced from ATCF-styled text output from the HFIP community tracker.

These products show the phase of the cyclone (e.g., warm- vs. cold-core) as well as highlight any significant transitions (e.g., tropical→extratropical) during the forecast period.

Symmetry (tilt): Shows evolution of the symmetry and magnitude of storm's warm/cold core.

Depth of warm/cold core: Shows the evolution of the depth and magnitude of the storm's warm/cold core.

Reference: Cyclone Phase Analysis and Forecast: Help Page

10-m wind structure

Produced from HFIP community tracker text output.

Shows the radial structure for both storm-relative and earth-relative 10-m winds for each quadrant of the cyclone. Note that the left panels have the x-axis go from 500→10 km, while the right panels have the x-axis go from 10→500 km (to illustrate the low-level wind field in a cyclone). All sub-tabs can be selected simply by moving the cursor over them.

Storm size

Produced from ATCF-styled text output from the HFIP community tracker.

Radius of maximum wind: [Top panel] Box plot time series of the radius of maximum wind (RMW), which is computed by the HFIP community "external" tracker. Time series of ensemble mean maximum surface wind speed are provided (thick gray line with square markers) to show the relationship between RMW and max wind speed over time. [Bottom panel] Spaghetti plots showing each member's radius of maximum wind every 6 hrs.

Radius of 34-, 50-, and 64-kt winds: Four figures are provided and can be viewed by clicking each sub-tab. The first figure shows an ensemble mean time series of 34-, 50-, and 64-kt wind radii. Color-coded numbers are annotated every 24 hrs to show how many members when into the ensemble mean calculation at that time. The final three figures show separate spaghetti plots of the 34-, 50-, and 64-kt wind radii. The ensemble mean is overlaid in red.

Regional-scale fields

Produced from HFIP GrADS scripts processing 1/6° (~18 km) grib data from the outer domain.

Each field is an average of the 16 GFDL hurricane ensemble members where member availability is at least 6 (40% threshold). Each of the HFIP regional plots are standardized (e.g., use predetermined domain locations, color schemes, contour intervals, and labeling) to allow for easier inter-model comparison on the HFIP Deterministic Model Output web site.

Surface fields:

  • Mean sea-level pressure (MSLP; mb) is contoured in solid black every 4 millibars.
  • 10-m winds (kts) are shown as blue wind barbs and are shaded corresponding to different TC intensity categories.
  • 1000—850-mb thickness (dm) is contoured in dashed red/blue every 1 decameter.

Combination fields:

  • 850-mb relative vorticity (x10-5 s-1) is shaded.
  • 500-mb geopotential height (dm) is contoured in solid black every 3 decameters.
  • 200-mb winds (kts) are shown as blue wind barbs.

850- and 500-mb fields:

  • Relative vorticity (x10-5 s-1) is shaded.
  • Geopotential height (dm) is contoured in solid black every 3 decameters.
  • Winds (kts) are shown as blue wind barbs.

700-mb fields:

  • 700—500-mb layer-averaged relative humidity (RH; %) is shaded.
  • Geopotential height (dm) is contoured in solid black every 3 decameters.
  • Winds (kts) are shown as blue wind barbs.

200-mb fields:

  • Relative vorticity (x10-5 s-1) is shaded.
  • Geopotential height (dm) is contoured in solid black every 6 decameters.
  • Winds (kts) are shown as blue wind barbs.

Storm-scale fields

Produced from HFIP GrADS scripts processing blended 1/12° (~9 km) and 1/6° (~18 km) grib data from the two innermost nests.

Each of the 16 GFDL hurricane ensemble members are included in these "postage stamp" plots. Similar storm-scale products from the other HFIP modeling groups can be found on the HFIP Deterministic Model Output web page.

Surface fields:

  • Mean sea-level pressure (MSLP; mb) is contoured in solid black every 4 millibars.
  • 10-m winds (kts) are shown as dark-gray wind barbs and are shaded corresponding to different TC intensity categories.

850-mb fields:

  • Relative vorticity (x10-5 s-1) is shaded.
  • Winds (kts) are shown as dark-gray wind barbs.
  • 1000—850-mb thickness (dm) is contoured in solid black every 1 decameter.

700-mb fields:

  • 700—500-mb layer-averaged relative humidity (RH; %) is shaded.
  • Geopotential height (dm) is contoured in solid blue every 3 decameters.
  • Winds (kts) are shown as dark-gray wind barbs.

200-mb fields:

  • Temperature anomaly (°C) is shaded.
  • Geopotential height (dm) is contoured in solid black every 6 decameters.
  • Winds (kts) are shown as dark-gray wind barbs.

Longitude-/Latitude-Height Cross Section I:

  • All cross sections are from 1000-100 mb and are centered on the cyclone.
  • Total horizontal wind is shown three ways: (1) shaded, (2) black wind barbs, and (3) solid black contours for each TC intensity category.

Longitude-/Latitude-Height Cross Section II:

  • All cross sections are from 1000-100 mb and are centered on the cyclone.
  • Relative humidity (RH; %) is shaded.
  • Temperature anomaly (°C) is contoured every 2° from -8 to 8°C, using solid blue for the negative values, and solid red for the positive values.
  • Relative vorticity (x10-5 s-1) is contoured in solid black at 50, 100, 200, 400, and 800.
  • Zonal/Meridional winds (kts) are shown as black wind barbs.

Integrated kinetic energy (IKE) and surge destructive potential (SDP)

Produced from HFIP community tracker text output.

Integrated kinetic energy (IKE) and surge destructive potential (SDP) are calculated based on Powell (BAMS, 2007) within a 400 km radius from the cyclone's center. IKE values are computed for tropical storm and hurricane threshold winds (i.e., > 18 m s-1 and > 33 m s-1, respectively), as well as for a low-end wind threshold of >10 m s-1. SDP ratings are based on the familiar 1-5 range of the Saffir-Simpson scale, with continuous fits to allow for storms as weak as 0.1 or as strong as 5.99. Both box plot and spaghetti plot time series are provided.

Reference: Hurricane Research Division: Integrated Kinetic Energy

Fractional wind

Produced from HFIP community tracker text output.

Fractional wind by quadrant: Box plots time series of the percentage of area covered in each quadrant by 34-, 50-, and 64-kt winds within a 400 km radius from the cyclone's center.

Fractional wind for all quadrants: As in the previous figure, except for all quadrants.

PDFs of the wind for all quadrants: Ensemble mean wind speed probability density functions (PDFs, within a 350 km radius from the cyclone's center) plotted every 24 hrs.

TC diagnostics

"Max sfc wind", "Min SLP", and "Radius of maximum wind" are produced from the ATCF-styled text output from the HFIP community tracker. All other parameters in this section are produced from HFIP model diagnostic files.

[Top panel] Box plot time series of TC diagnostics every 6 hrs. The number of members present (out of 16) in the box plot calculations at each 24-hr interval is shown in parentheses. [Bottom panel] Spaghetti plots of TC diagnostics every 6 hrs. The percentage of dissipated members is shown in parentheses at each 24-hr interval. An ensemble track plot is provided below each diagnostic product for reference to forecasted cyclone location.

Radii* used in area averages
850-200 mb shear:0-500 km
200 mb temperature:200-800 km
850 mb tangential wind:0-600 km
850 mb vorticity:0-1000 km
200 mb divergence:0-1000 km
Sea surface temperature:0-50 km

*Around storm center


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A note about box plots: Box plot time series are used to show not only the ensemble mean, but also the degree of spread among the members. The ensemble mean is shown by a thick (usually red) line with square markers. Extreme values are shown by vertical lines terminating with horizontal dashes. Unfilled boxes show ±1 standard deviation (represented by the symbol σ), which is a measure of how spread out the data are.


References


Research Team Members

    (Timothy.Marchok@noaa.gov) - Principal Investigator

    (Matthew.Morin@noaa.gov) - Website Developer / Research Scientist

    (Morris.Bender@noaa.gov) - Senior Research Scientist