NWS Jacksonville » Weather Stories » Using GFE to Generate Marine Forecasts
Using IFPS/GFE to Generate Marine Forecasts for Northeast Florida and Southeast Georgia Coastal Waters
by Andrew Shashy
(Meteorologist, National Weather Service Jacksonville)
Over the past several years, the NWS has continued to develop the Interactive Forecast Preparation System (IFPS), which allows weather forecasters to prepare a forecast using gridded information. The IFPS system has been in operation since fall of 2002. This system has been part of the NWS modernization program and has created a new way of presenting and developing better marine forecasts at the Weather Forecast Office (WFO) level.
Using the IFPS has changed the way forecasters create marine forecasts. Before IFPS, forecasters would typically examine which computer models would best represent expected weather conditions over the next few days going back and forth looking at model output for winds and seas, and then translating this into a text forecast. Since the new IFPS technology came to the WFO, the forecast process has become more detailed and methodical. The first step usually begins with interrogating numerical model information and/or populating objective wind analyses into the gridded database and closely examining model forecasts. Second, one or more numerical gridded fields are loaded into the database sometimes using a weighting smart tool to put more emphasis on one model over another. When wind grids are edited in the system, it can be a time-consuming task not only to correct model deficiencies, but also to collaborate with neighboring weather offices. Creating wave grids can also be a time-consuming task due to poor model resolution and initialization of the current sea state. See the image below from the GFE.
Adjustments to wave forecasts may also be needed where wind grids are changed from what is forecasted in the Global Forecast System (GFS) model, which is the primary wind input to the Western North Atlantic Wave model (WNA). For instance, on many occasions the GFS model under-forecasts nocturnal southwest flow events during the summer months, which can be upwards of 20 to 25 knots. For this reason, wind speeds as well the sea state would need to be increased by the marine forecaster. Simple pencil edits tools and adjustments to the wind speeds can fix these types of biases. These types of problems were usually not well understood or documented before IFPS, but now with gridded wind and sea state guidance, the forecast process has become somewhat easier by focusing more on the model output information instead spending a lot of time writing textual forecast. Another advantage to the gridded forecast information is that if a forecaster believes the previous model run of the GFS was superior to the current one, he or she can load it into the GFE to use as a base wind grid in combination with the previous forecaster's grids. Another situation where numerical wave models suffer some skill is in the nearshore waters where shoaling and wave dissipation are difficult to numerically model. In addition, model guidance is smoothed and not well depicted between the transition zone of land and sea. Therefore, adjustments are sometimes needed over the near shore waters. Experienced marine forecasters can now apply this gridded database knowledge to develop improved forecasts for marine community. See the example below of a graphical marine forecast:
Although there is a better forecasting process and better computer models in which to forecast for the coastal waters, it does not replace the importance of initialization, or also known as a starting position of what is going on at the present time. Ships, buoys, NOAA satellite imagery are all sources of information that help give ground truth to the current state of the atmosphere. When boaters and the shipping industry call on the NWS about weather forecasts, they may be able to tell forecasters important and up-to-date information, such as the visibility in dense fog events or general information such as the wind speed. This information can help a great deal for the forecaster to determine which model may be performing better and whether advisories need to be issued. So a question one may ask is: How much have marine forecasts improved since the implementation of IFPS? Based on statistics from just a couple of coastal observations in Northeast Florida, percent correct of wind speed forecasts increased from 73% to about 81% after IFPS was implemented. It is also worth noting that fairly significant improvement was noted near the lower limits of small craft advisory wind speed range, which in the 18 to 22 knot range.
In summary, the NWS has created new and advanced ways of generating not only text forecasts but graphical marine forecasts for the end user. Numerous tools at the hands of the forecaster, such as model blends and consensus forecasts along with corrections to known biases can help improve marine forecasters. Better forecasts and improved advisory and warning decisions will almost certainly provide a better service to the marine community. The graphical forecasts are updated at least twice per day and are available at the NWS Jacksonville website noted here: http://www.weather.gov/forecasts/wfo/sectors/jaxMarineDay.php#tabs. Finally, point and click marine forecasts can be retrieved from the JAX website that produce more specific forecasts for any location within 60 nm of the coastline.