949 NOUS41 KNHC 131254 PNSNHC Public Information Statement NWS National Hurricane Center Miami FL 900 AM EDT Thu Sep 13 2018 To: Subscribers: -NOAA Weather Wire Service -Emergency Managers Weather Information Network -NOAAPORT Other NWS Partners and NWS Employees From: Allison Allen Chief, Marine, Tropical and Tsunami Services Branch Subject: Alerting Partners to the Potential for Non-Sequential Tropical Cyclone (TC) Storm Numbering in the Atlantic Basin Effective Immediately This Public Information Statement is intended to alert users of National Weather Service (NWS) TC products that non-sequential numbering of TCs in the Atlantic basin may be necessary. NWSI 10-601: "Tropical Cyclone Forecast Center Products" details storm numbering and naming conventions in Section 3, which explains that all systems requiring advisory packages (i.e., TCs or potential TCs, whether tropical or subtropical) will be sequentially numbered within their basin of origin. NWSI 10-607: "Tropical Cyclone Advisory Products" can be found here: http://www.nws.noaa.gov/directives/sym/pd01006007curr.pdf TC advisory products from the National Hurricane Center include: PRODUCT AWIPS PIL* WMO HEADER --------- --------- ---------- TC Public Advisory TCPAT/1-5/ WTNT/31-35/ KNHC TC Wind Speed Probabilities PWSAT/1-5/ FONT/11-15/ KNHC TC Forecast / Advisory TCMAT/1-5/ WTNT/21-25/ KNHC TC Discussion TCDAT/1-5/ WTNT/41-45/ KNHC National TC VTEC Product TCVAT/1-5/ WTNT/81-85/ KNHC TC Update TCUAT/1-5/ WTNT/61-65/ KNHC Aviation TC Advisory Message TCANT/1-5/ FKNT/21-25/ KNHC * AWIPS PIL - AWIPS Product Identifier Label These products use five distinct "bins" (i.e., AWIPS PILs and WMO Headers that vary only by the last digit which is a numerical value 1-5). The bins are used in sequential order such that the first system requiring advisory packages in the Atlantic basin is storm number AL01 and has products with AWIPS PILs and WMO headers ending in 1 (i.e., bin 1), the second system (AL02) has products ending in 2, etc. The sixth system of the year (AL06) in a particular basin will have products that end in 1, cycling back to the beginning of the bin numbers as all of the bin numbers up to that point (i.e., 1-5) have recently been used. However, there is a complication in the 2018 hurricane season. Hurricane Florence has the storm number AL06 and is using AWIPS PILs and WMO headers ending with "1". Currently, advisories are being written for systems ending with "3", "4", and "5", for Helene (AL08), Isaac (AL09), and Joyce (AL10), respectively. The next system in the Atlantic would normally be AL11, which would usually correspond to AWIPS PILs and WMO headers ending with "1". However, products for Hurricane Florence are already using these AWIPS PILs and WMO headers. If another TC, potential TC, or subtropical cyclone forms in the Atlantic basin before advisory packages are discontinued for Florence, it will have AWIPS PILs and WMO headers ending with "2" and will be numbered AL12. The AWIPS TC software used by the NWS Weather Forecast Offices (WFOs) assumes a strict relationship between the storm ID and the bin number. If the storm number AL11 was used while advisories are still being written on Hurricane Florence, advisory products for AL11 would be assumed by this software to use the exact same AWIPS PILs and WMO headers as Florence. Given this assumption and possible NWS user software dependencies on the expected relationship between storm number and the AWIPS PIL/WMO header, storm number AL11 will need to be skipped in order to ensure no conflict with Hurricane Florence advisory products. If this occurs, NHC will provide an explanation of the issue in the Tropical Cyclone Discussion product for the new storm. Questions should be directed to: Jessica Schauer NWS Tropical Services Program Leader NWS Marine, Tropical and Tsunami Services Branch Miami, FL 33165 Telephone: 305-229-4476 Email: Tropical.Program@noaa.gov Or Dr. Michael Brennan Branch Chief, Hurricane Specialist Unit National Hurricane Center Miami, FL 33165 Telephone: 305-229-4436 Email: Michael.J.Brennan@noaa.gov National Public Information Statements are online at: https://www.weather.gov/notification