This document details the recent changes to the Automated TRaP which became operational on April 10, 2007 and is based on an e-mail issued at the beginning of April, 2007.

Previously, notification of a new TRaP was made when a tropical cyclone with a current intensity of at least 35 knots (T2.5 on the Dvorak scale) was within 24 to perhaps as many as 36 hours from impacting land and only after an experienced analyst had approved it. Under full automation, we will retain the tropical depression intensity as the minimal intensity for which a TRaP will be generated and no TRaPs will be produced for “tropical disturbances” or “tropical lows” because the associated convection is more likely to undergo rapid and frequent changes in intensity and areal coverage.

TRaPs will be generated using forecast bulletins from the Regional Specialized Meteorological Centers (RSMC) at Miami, Honolulu, Tokyo, La Reunion, Perth, Darwin, Brisbane and Nadi and/or from the U.S. Joint Typhoon Warning Center (JTWC). TRaPs will be updated whenever a new forecast or new rain rate data becomes available with the restriction that the rain rate data must be within 3 hours of the synoptic time associated with the forecast (i.e., 00Z, 06Z, 12Z and 18Z) and the rain rate data covers most, if not all, of the storm. E-mail notification will be made every two hours of all TRaPs that have been created within your area of responsibility regardless of their location within the basin.

To accommodate the significant increase in the number of TRaPs disseminated we have renovated our web page. The new page can be viewed at http://www.ssd.noaa.gov/PS/TROP/trap.html. The TRaP shown on this page will be the most recent regardless of basin and will remain on the page until updated with new information.

The front page will always be the most recent TRaP generated. The left side will list the active storms by basin. Clicking on an active storm link will take you to the storm page which prominently displays a table or tables containing links to graphs of the rain rate, rainfall amounts in 6-hour increments and the 24-hour total rainfall amount by microwave sensor. The time contained in the link represents the time of the rain rate data over the storm. The label above the table provides the agency whose track forecast was used in generating the TRaP. At the bottom left hand corner are buttons to access the archives.

Due to differences in the convention used to number tropical cyclones between JTWC and the RSMCs the web page may at times contain separate links for what is, in fact, the same system. For example, RSMC Reunion may be warning on tropical depression “12” which JTWC is carrying as 15S. The storm page for “12” would show TRaPs generated from Reunion forecast bulletins while the table for TRaPs generated for “12” by JTWC will contain the words “Awaiting Data.” The opposite would be true for the storm page for 15S. Once the RSMC has named a tropical cyclone and that name is reflected in the bulletins by JTWC, the TRaPs generated by both agencies will appear on the storm page bearing the RSMC’s name for the system.

We have made every effort to include logic in the automation process that will prevent TRaPs from being generated in the event of a blank or partial microwave pass, but we cannot guarantee that there will be some that make it through since the TRaPs will no longer be vetted by an analyst. This is just one reason that it is important for you to review the weaknesses inherent in the TRaP process since full automation means that each of you will have to assess the TRaPs.

• TRaPs should only be used when the rain area covers the entire storm and is not fragmented, as might occur when a system is close to land (so-called “coastline contamination” recently corrected in AMSU, but still occurring with SSMI).
• It has been observed that TRaPs do not verify well when the system is sheared or changing speed and/or direction abruptly.
• More care should be considered for TRaPs that change by 50% or more in a 12-24 hour period. Such may be the case with tropical depressions and even weak tropical storms in which convection is more likely to undergo rapid and frequent changes in areal coverage. As a general rule of thumb, if the storm has intensified (weakened) and the TRaP has increased (decreased) significantly (> 50%) in the past 24 hours, it is best to use the current TRaP. If there has not been much change in intensity during the last 24 hours the user will have to make a judgment as to which TRaP to use.
• TRaPs do not include orographics.
• TRaPs do not verify well when tropical cyclones are interacting with synoptic scale features such as fronts and shear lines.
• The TRaP is dependent, in part, on an accurate forecast of the tropical cyclone’s speed and direction of motion.
• The TRaP assumes that the storm structure and rain rates remain constant over the 24 hour period. In this sense, TRaP might be expected to perform best on a tropical cyclone that is in a steady state.

An online tutorial describing the TRaP technique has been developed by NESDIS’ Sheldon Kusselson and produced by the Cooperative Program for Operational Meteorology, Education and Training (COMET) and can be found at http://meted.ucar.edu/npoess/trap/. Even though the tutorial has not be updated for the new automated TRaP process, all users are still strongly urged to review the material.

E-mail Mike Turk, NOAA/NESDIS/Satellite Analysis Branch, to be included in automated notification or with questions and comments.

Validation Links:

Australia Validation (pdf)

Comet TRaP tele-training from July 2003 (power point presentation)

Taiwan Validation (power point presentation)

The Tropical Rainfall Potential Technique Part 1 - Description; Part 2 - Validation (pdf)

US Validation Part 1, Part 2 (pdf)