On July 8, the Joint Typhoon Warning Center (JTWC) introduced a new forecast product to the DOD community - the Two-Week Tropical Cyclone Formation Outlook. This outlook highlights geographic areas forecasters consider suspect for potential formation of a significant tropical cyclone.
The new product covers the western North Pacific Ocean, the north and south Indian Ocean, and South Pacific Ocean basins based on environmental factors and development indicators in several deterministic and ensemble weather models. Highlighted locations are referred to as “Potential Formation Areas (PFAs).”
“We are proud to be on the forefront of research and development. While we continue to make progress on track, intensity and wind radius forecasting accuracy through 120 hours, predicting tropical cyclogenesis up to two weeks in advance of development is still a challenge in the tropical cyclone forecasting community. My team is excited to debut this product that will provide our decision-makers with an outlook for long-term planning and use for asymmetrical advantage,” said JTWC Commanding Officer Commander Jillene Bushnell.
The two-week outlook is issued twice daily, at 0000Z and 1200Z, and may also be reissued at the top of any hour if significant changes have occurred with existing systems. Organized convection, or thunderstorms, may not yet be present in a PFA, but the environment is expected to be conducive to tropical cyclone genesis during the specified timeframe. PFAs are removed from the outlook when forecasters either consider tropical cyclone formation unlikely or when a tropical cyclone warning is issued on an area covered by the PFA.
If you follow JTWC’s forecasting, you may know that there are “investigation areas” discussed on the Significant Tropical Weather Advisory bulletins. These bulletins assess a tropical disturbance’s probability of developing into a tropical cyclone within 24 hours. The PFA probability must be equal to or can be higher than the invest area, because PFAs cover a longer timeframe.
The forecaster’s goal is to identify and designate potential tropical cyclone formation areas that are well-handled by multiple numerical forecast models and other data sources as early as possible. During testing from March through early July 2018, 100% of developing cyclones were located within PFAs prior to intensifying. About one-half of the formation areas were identified at least five days in advance of the formation time. However, because not all formations can be predicted early based on environmental predisposition alone, the absence of a potential TC formation area from any basin or region, particularly at long lead time (greater than 5 days), should not be interpreted as a “zero threat” indicator.
The outlooks feature two primary graphical products--the Two-Week Formation Outlook graphic that provides a large-scale illustration of potential formation areas and the PFA Status graphics that provide zoomed in views of each area and shows the predicted development timeline and probability, with the probability category indicated by the color of the box.
Forecasters use objective measures to subjectively determine development probability; the thresholds are <40% for low probability (yellow box), 40-60% for medium probability (orange box), and >60% for high probability (red box). Boxes encompass the area where tropical cyclone formation is likely to occur. As with many weather related predictions, the further out the forecast, the larger the uncertainty, and therefore, the larger the PFA box will be.
Generally, if several models develop a circulation, the time to formation is shorter, and the Madden-Julian Oscillation (MJO) signal is favorable, the probability for development will be higher and the box will be smaller. The MJO is a well-known large-scale phenomenon on a 30 to 60-day cycle that causes major fluctuations in thunderstorm activity in the deep tropics.
The Two-Week Tropical Cyclone Formation Outlook is available through the JTWC’s CAC-enabled website (https://pzal.nmci.navy.mil) in the Tropical Cyclone Support drop-down menu. Greater detail on the objective measures used to forecast can be found on the “Product Overview and FAQs” in this section of the website.
JTWC (Task Element 80.7.7.1) is jointly staffed by U.S. Navy and Air Force personnel and falls under the operational control of Commander, Task Group 80.7/Commander, Naval Meteorology and Oceanography Command via Fleet Weather Center San Diego (Task Unit 80.7.7). U.S. Air Force personnel are administratively assigned to the 17th Operational Weather Squadron, a subordinate squadron of the 1st Weather Group and the 557th Weather Wing.
JTWC provides tropical cyclone reconnaissance, forecast, warning and decision support services for operational advantage to U.S. government agencies operating in the Pacific and Indian Oceans. Navy personnel at JTWC also provide tsunami advisory information and recommendations to shore installations and units, as well as impact forecasts for U.S. Pacific Fleet’s airborne Intelligence, Surveillance and Reconnaissance and decision support services to U.S. Pacific Command and its subordinate commands.
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