How meteorologists track and forecast typhoon paths
Posted by mandyf on September 22, 2011
The way that meteorologists track and forecast typhoons is a rather unique and sometimes very intense process which relies on many people contributing rather than just one. In this article we won’t be discussing forecasting or tracking in the manner television meteorologists do it, it will be a a first hand account of the way an actual warning center works through handling this phenomena.
Until the late 1990’s the forecasting and tracking of typhoons fell under the eye of the Joint Typhoon Warning Center (JTWC) located on Nimitz Hill in Guam. While they still do this, operations are now located in Hawaii. JTWC is made up of U.S. Navy and Air Force personnel who fill a variety roles all aimed at putting out the best forecast possible to safeguard some 53 million square miles of the Earth. Depending on operational needs, this is sometimes expanded. For those who aren’t quite sure what a typhoon is, it is simply the name assigned to a hurricane that forms west of the International Date line in the Northwest Pacific Ocean.
While two sections carry out the bulk of the work surrounding the actual forecast, there are many players that make it all possible. NEDS (Navy Environmental Data System) operators download charts, and satellite photos which are provided by Air Force personnel attached to the DMSP (Defense Meteorological Satellite Program) who task the “birds” to take photos. Air Force Satellite Analysts (SA) perform computer fixes of a system (Eye fixes are possible when necessary) which help define the size and organization of a system. Typhoon Duty Assistants (TDA) gather and plot a combination of synoptic and upper air data to charts for the 850mb and 200mb (Surface and upper air) levels on which a streamline analysis is performed. The Typhoon Duty Officer (TDO) generally performs the analysis of these charts although SA’s and some TDA’s are also qualified for the task. The TDO is also responsible for studying a number of computer generated models like the PAC’s BAM’s, CSUM, CLPR, RCV (Recurve), and Blend/Weighted amongst others. As if that weren’t enough they also study NED’s charts and previous synoptic data and satellite photos to help gain a perspective on a systems movement and growth.
Every twelve hours either an ABIO (Abbreviated Indian Ocean Update) or ABPW (Abbreviate Pacific West Update) is sent out to all product users, (Military Installations, U.S, Navy Ships, and Merchant Vessels) which basically describes what activity if any is in that area. These are also generally the first time a potential system may be mentioned. Once a a potential system is spotted, the team watches it to see if it organizes and intensifies. If it reaches 25 kts. a TCFA (Tropical Cyclone Formation Alert) is issued which notes that the system is of heightened interest and will be watched for the potential to develop to a Tropical Disturbance (TD). Once a system becomes a Tropical Disturbance official warnings are issued every 6 hours assuming it is in the North West Pacific (NWP).
At this point there are basically only three paths a storm will follow: Straight, Recurve, and Northward. Systems that follow a straight path generally head to the Phillipipines, Taiwan or Vietnam. Northward storms generally do as their name suggests and will usually only impact the Marshall and/or Marianas islands. Recurve storms are the tricky ones as they can take on almost any area but generally target Japan, Korea, Taiwan and China although the Phillipipines has seen a few brutal ones. Figuring out what path a storm will take early on is no easy task, and with forecasts ranging 72 hours in advance the possibility for error can be tremendous.
As the system organizes it becomes even more difficult to figure out in some cases. Some will flow forward rather smoothly while others begin a stair step type pattern. At times a system will stall or “sit n’ spin” for a few hours or even upwards of a day, still moving, just very slowly while it feeds off a warm water source. This is something almost impossible to predict as is what the system will do when it begins moving on again. When a storm stalls and feeds, it grows rapidly in terms of a system and while ragged at first, it can collect itself rather quickly and go off on almost any course with it’s new found strength. Imagine a merry-go-round getting a shot of adrenaline and that is what a forecaster is dealing with.
Add all of this to the fact that nature is really never truly predictable and what much of the process comes down to in the end is a combination of hard data, gut instinct, and a knowledge of history. Knowing what similar sized storms that originated and followed the same path to that point in the past did is invaluable. Finally when the TDO has digested everything presented to him, he has to choose what aides have the best grip on the storm based on satellite imagery, synoptic data, and history. He then prepares the warning along with a prognostic reasoning which details how the conclusion for that forecast was reached. The message is then encoded and disseminated electronically and by hard copy for in house users.
This cannot be complete without saying that among those already named, countless observers, forecasters, pilots/navigators on aircrafts, and military/merchant seaman vessel personnel all aid in the process. They provide data both scientific and at times first hand of what is going on where they are. All of this information helps create a comprehensive picture of the macro-climate. As each system in the basin in one way or another has some effect on the others either by creating ridges, buffer zones, or even twin systems, everything is valuable. That is what goes into tracking and forecasting a typhoon.