Note: HRES and Ensemble Control Forecast are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

Tropical Cyclone diagrams - existing TCs

Tropical Cyclone Products

Products are generated for all tropical cyclones that have been officially observed (by a Regional Specialized Meteorological Center (RSMC)) at the initial time of the forecast.  Both the strike probability charts and the Lagrangian meteograms (i.e. following the tropical cyclone forecast positions) are dependent on these official reports from around the world and do not take tropical cyclone genesis into account.   The available charts are:

  • Cyclone position:

Once official reports signify the existence of a tropical cyclone, it is automatically tracked.  The tracking algorithm uses Ensemble Control Forecast output and is based on using the extrapolation of past movement and the mid-tropospheric steering flow to obtain a first-guess position 6 hours into the future.  The actual forecast position is then determined by searching for mean sea level pressure (MSLP) and 850hPa vorticity extremes around the first-guess position.  In some circumstances the thickness maximum, the central MSLP, surface winds, and the orography are also considered in the evaluation.  This process repeats at 6 hour intervals through the forecast until either the tropical cyclone dies or the end of day10 is reached.

When two Tropical Storms are relatively close the possibility arises that the tracking algorithm may jump from one to another - e.g. if one is decaying (see Fig8.1.16.1-9).  This seems to be a very rare occurrence and which is under investigation, but users should be aware of the potential for this error.

  • Strike probability charts:

Strike probability is defined as the proportion of members that predict that the tropical cyclone will pass within a 120km radius of a given location at any time during the next five days.  In other words, the time dimension is integrated over the forecast range (see Fig8.1.16.1-2).  This allows for a quick assessment of high-risk areas, regardless of the exact timing.  A 40% probability at a specific location means that approximately 40% of ensemble members place that particular tropical cyclone centre within a 120km radius of that location at some point during the coming 10 days.  If a tropical cyclone is forecast to loop back on itself, and so pass close to the same location two or more times, as happens occasionally, the probability shown on the plot will be the highest probability encountered in any given 6h time interval during the forecast period.

  • Lagrangian meteograms:

Lagrangian meteograms are a convenient way of evaluating the forecast for a specific tropical cyclone.  They contain time series of the central pressure and of the 10m wind speed maximum predicted within a 7ºx7º lat-long box centred on the cyclone and following its motion in each forecast member.   The "box and whisker" symbols are similar to those used on the Ensemble Meteograms.  However, unlike the standard meteograms, the number of ensemble members represented by the boxes and whiskers varies, and can be assessed by reference to the strike probability chart or individual forecast trajectories chart.


Fig8.1.16.1-1: To view tropical cyclone forecasts:

  1. On the charts page, click on latest tropical cyclones.
  2. On the tropical cyclones page find the WMO region of interest.
  3. Select cyclone of interest (either on chart or by name).  Position shown at analysis time.  Can select product display option at this stage or later.
  4. Display of product (in this case Strike Probability - probability that Nepartak will pass within 120km radius, with probabilities for cyclone intensity and Lagrangian meteograms of maximum associated 10m mean wind speed and central pressure).

A quick-look graphical guide to interpreting these products is available.

Examples of IFS and AIFS Ensemble Forecasts of tropical cyclone products

On web site

Tropical Storm Products for Typhoon Bavi  over the east Pacific in the summer of 2026. 

Fig8.1.16.1-1: IFS Strike probability chart for Bavi DT 00UTC 03 Jul 2026. 

Colours show the proportion of members that predict that the centre of Typhoon Bavi will pass within a 120km radius at any time during the next five days.   Ensemble mean (dotted line) and Ensemble Control (solid line).  Top right: Ensemble probabilities (not including or ensemble control) for the intensity of this tropical cyclone to fall into each of the 5 tropical cyclone intensity categories shown at 6hr intervals to 10 days.  Ensemble members are shown below the chart in the colours of the intensity of the Tropical Cyclone.Centre.   Centre and Bottom (right):  Lagrangian meteogram of the distribution the full ensemble (in box and whisker format), the ensemble mean (dotted line) and ensemble control (solid line) for the maximum 10m mean wind speed (kt) associated with Typhoon Bavi , also MSLP (hPa) at the Typhoon Bavi pressure centre.  Note the categories used on the top panel are derived on the basis of the variable shown on the middle panel.

 

Fig8.1.16.1-2:  Individual ensemble and ensemble control (black line) forecast trajectories of the centre of Typhoon Bavi for IFS (left) and AIFS (right) DT 00UTC 03 Jul 2026.  Ensemble members are shown below the charts in the colours of the intensity of the Tropical Cyclone.   The colours on each trajectory represent 24hr forecast time periods.

In this case IFS forecast an intense Typhoon (many ensemble members shown black).  AIFS forecast a weaker system (ensemble members almost uniformly shown orange ), but this is probably due to the AIFS coarser grid length (0.5 deg lat) compared to IFS grid length (9km).

Tropical Storm Products for Narelle passing over Northern Australia in the spring of 2026. 

Fig8.1.16.1-3: IFS Strike probability chart for Narelle DT 12UTC 19 Mar 2026.  Colours, tracks, intensities, and box and whisker plots as described under Fig8.1.16.1-1. 


Fig8.1.16.1-4: AIFS Strike probability chart for Narelle DT 12UTC 19 Mar 2026.  Colours, tracks, intensities, and box and whisker plots as described under Fig8.1.16.1-1.

In this case IFS forecast the Tropical Cyclone to intensify at times to a vigorous typhoon (some ensemble members shown black) with interludes (mainly over land) of decreased intensity (many ensemble members shown orange or red).  AIFS forecast a weaker system (ensemble members almost uniformly shown orange ), but this is probably due to the AIFS coarser grid length (0.5 deg lat) compared to IFS grid length (9km).  AIFS correctly predicted the track to curve back into Western Australia (IFS forecast the system to move into the Indian Ocean).  IFS better predicted the intensity and variation in strength the system.



Fig8.1.16.1-5: Web chart of tropical cyclone activity (Including genesis) showing typhoon strike probability.  The web chart is clickable; a click at any location gives meteograms, plumes, wavegrams or  extreme forecast indices (EFI) and Cumulative distribution functions (CDF) for 2m temperature, rainfall and 24hr maximum wind gust.  Forecast DT 00UTC 21 Aug 2026, VT 00UTC 26 Aug 2026.

Fig8.1.16.1-6: Sample meteogram, CDFs/EFIs, wavegram, and  wave spectrum at a point off the east coast of Okinawa for the same time as shown in Fig8.1.16.1-5.

During passage of the typhoon:

  • Meteogram: Mean rainfall is quite low at 5mm/6hr, but some ensemble members show above 60mm/6hr with a max of 142mm/6hr.  Mean wind 15m/s but Ensemble Control and one member show 35-45m/s.
  • CDF and EFI graphs: Most ensemble members show forecasts distribution of rainfall below M-climate distribution some with little precipitation, but a few members are extreme and extreme forecast index EFI for 24hr rainfall is fairly high at 53%.  Similarly with max gusts where the forecasts distribution is lower than M-climate distribution but some values are extreme and EFI is high at 82%.  Mean temperatures lie closely near the M-climate distribution and EFI is near 0%.
  • Wavegram:  Significant wave height reaches a mean of 7m with a couple of ensemble members predicting 12-14m.  A long slow swell with period of 12s precedes the arrival of the typhoon.
  • Wave Spectrum diagram: High energy (high variance density) waves arrive from the SE with a 0.8Hz (~12s period). The innate difficulties of correctly representing the winds around tropical cyclones impacts upon the representation of waves nearby.

Fig8.1.16.1-7: Comparing IFS and AIFS output of Tropical Cyclone Activity.  DT00UTC 24 Aug 2026, VT00UTC 27 Aug 2026.      AIFS produces weaker systems than IFS because of the difference in resolution.  AIFS has coarser grid length (0.5 deg lat) compared to IFS grid length (9km).  This means that in some cases tropical systems may differ on the two charts and in some cases may not appear on both charts at all.  In this case Typhoon Saudel is not captured at all by AIFS.

Note: A click on a location on AIFS charts gives IFS meteograms etc, not AIFS output. 

On ecCharts

Tropical cyclone activity charts for named or pre-existing tropical cyclones are also available on ecCharts.  The information can be combined with other significant weather parameters (e.g. 10m winds, significant wave height, etc).

 

Fig8.1.16.1-8: ecChart showing the ensemble member tracks of Typhoon Saudel up to VT 00UTC 25 Aug 2026 (T+120).  Trajectories show forecast tracks of the centre during the forecast period by ensemble forecast members (green) and Ensemble Control (red).  The spread of trajectories gives an indication of confidence in the trajectory - quite high in this case for five days ahead.  Trajectories are faded at earlier times in the forecast.    DT 12UTC 20 Aug 2026.


   

Fig8.1.16.1-9A: Precipitation and surface isobaric forecast NW Australia and NE Indian Ocean T+156 VT12UTC 29 Feb 2020.  TC Ferdinand is moving slowly off NW Australia and weakening.  TC Esther is moving towards the SW and strengthening.  

Fig8.1.16.1-9B: Locations of TC Ferdinand from HRES forecast DT 00UTC 23 Feb 2020 (solid line on chart).  At 12UTC 29 Feb 2020 the algorithm incorrectly identifies the location of Ferdinand at the location of TC Esther and subsequently follows the movement and developments of TC Esther.  The forecast values of ensemble mean and ensemble probabilities do not suffer from the same problem.


RSMC official forecasts of tropical cyclones take precedence

Note: IFS products on these pages regarding tropical cyclones are generated automatically without any editing by forecast experts.   RSMCs (Regional Specialized Meteorological Centres) have ultimate responsibility for official forecasts of tropical cyclones within their respective regions (ECMWF is one of a number of centres that provide data to them).  Up-to-date information is available by direct access to official RSMC forecasts through the WMO Severe Weather Information Centre.  For up-to-date forecast information for their own local area users should refer to forecasts from their own National Meteorological Service.

Additional Sources of Information

(Note: In older material there may be references to issues that have subsequently been addressed)


(FUG associated with Cy50r1)