NOTE: All products on these pages are experimental and should NOT be considered an official forecast. Please refer to the National Hurricane Center for official forecasts.
This website provides experimental 48 h and 120 h tropical cyclone (TC) genesis probabilities based on genesis forecasts from global numerical models. The genesis probabilities are based on logistic regression models that were developed for each global model and each basin. Genesis probabilities based on forecasts from the CMC, GFS, and UKMET are available for the 00Z and 12Z initialization cycles (only GFS for 06Z and 18Z cycles).
0-48 HR OUTLOOK
The image on the front page (0-48 HR OUTLOOK) is meant to be an overview and shows genesis forecasts from all models available in the current model initialization cycle. When a TC genesis event is identified, this image shows the model(s) which predict(s) genesis, the location of genesis, and a categorical probability of genesis. More detailed genesis forecasts from each model are plotted on the individual model graphics pages and model text output pages (more details below). As output from each model becomes available, the model name will display under the 'Models available in current run cycle' banner. In the example below, all 3 models are analyzing Hurricane Amanda (blue shapes) and the CMC is predicting a genesis event at 12N 95W, which has a low probability of genesis with 48 h (yellow square).
0-120 HR OUTLOOK
The image on this page is the same as the "0-48 HR OUTLOOK", except the genesis probabilities are for genesis within 120 h.
INDIVIDUAL MODEL GRAPHICS
For the more detailed information, click a model name on the left toolbar. When a TC genesis event is identified, the forecast genesis location is plotted, along with the 48 or 120 hour genesis probability. The global model forecast track is also shown.
MULTI-MODEL CONSENSUS FORECASTS
The "CONSENSUS" pages show the average location of TC genesis when 2 or more models indicate TC genesis with 5 degrees lat/lon of each other. They also show the probability of genesis at any time within 48 or 120 hours. Note that when multiple models predict the same TC, the probability of genesis increases. In the example below, the CMC, GFS, and UKMET all predict the same genesis event.
DEFINING A TC IN THE MODEL FORECAST FIELDS
Each forecast of TC genesis that appears in the graphics pages (described above) is a result of several criteria being met. Specifically, for each model initialization cycle, the TC identification algorithm searches for:
1. A relative minimum in mean sea level pressure (MSLP) with at least one closed isobar at a 2mb interval.
2. A relative maximum in 850mb relative vorticity which is horizontally displaced less than 2 degrees lat/lon from the MSLP minimum.*
3. A relative maximum in 250-850mb thickness which is horiztonally displaced less than 2 degrees lat/lon from the MSLP minimum.*
4. The maximum wind speed at 925mb at any point less than 5 degrees lat/lon from the MSLP minimum.*
*Indicates that a threshold value must be exceeded.
If criteria 1-4 are met for at least one forecast time (e.g., forecast hour 12), then we would classify this as a 'tropical disturbance.' However, if criteria 1-4 exist for at least 24 consecutive forecast hours in the model cycle (e.g., forecast hours 12, 18, 24, 30, 36), then we would classify the system as a 'tropical cyclone' with a genesis time at forecast hour 12. This distinction is important for the text output pages (described in the next section).
INDIVIDUAL MODEL TEXT OUTPUT PAGES
Each model text page has three products: "Tropical Disturbance Information," "Tropical Cyclone Information," and "Model-Indicated TC History."
To provide added detail, the "Tropical Disturbance Information" page displays the values of the aforementioned criteria 1-4 (i.e., MSLP minimum, 850mb relative vorticity, 250-850mb thickness, and 925mb wind speed maxima) and the values of the predictors that went into the regression model for each 6 hour forecast time step. This gives the user insight into why an area of low pressure may not have been classified as a TC according to our algorithm. It also helps explain the genesis probability values for areas of low pressure that do meet the TC criteria.
The "Tropical Cyclone Information" page provides the forecast genesis time and location, as well as the 48 and 120 h genesis probability. This is intended to be a quick-reference or summary product.
The "Model-Indicated TC History" page shows all genesis times, locations, and probabilities for each model-indicated TC. It gives the user information regarding how consistent a model has been at predicting genesis for a given system and how the genesis probabilities have evolved.
To depict how our regression-based probabilities are performing in real-time, we provide season-to-date verification products at the "THIS SEASON" link under the "VERIFICATION" tab. The geographic plots show the locations of genesis events. The colors reflect the genesis probability. The events are plotted as a filled circle when genesis did occur and as an open circle when genesis did not occur. Reliability diagrams are also provided. We caution that small sample sizes, especially at the beginning of the season, will limit the usefulness of the reliability diagrams.
Reliability diagrams for the 2013 season and the 2011-2013 seasonal average are available at the "HISTORICAL" link under the "VERIFICATION" tab.