OFFICIAL STATEMENT OF DOST-PAGASA ON THE HEAVY RAINFALL EVENT ASSOCIAT
16 January 2019
This is to clarify claims of “wrong forecasts and late warnings” on the heavy rainfall event associated with Tropical Depression (TD) Usman as alleged by the following:
1. Dr. Mahar Lagmay on his Facebook account dated 04 January 2019 entitled, “Simpleng analysis kung bakit maraming namatay sa Bicol dahilsa #UsmanPH”, further quoted by different media sources, as follows:
In response, although his above-stated definition is correct in terms of PAGASA’s hourly rainfall intensity classification as per PAGASA Memorandum dated 20 June 2012, PAGASA defines moderate and heavy rainfall in its Severe Weather Bulletins (SWBs) as 24-hour (daily) accumulated rainfall of 60 to 180 mm and more than 180 mm, respectively. The forecasts for 28 – 29 December 2018 indicated the “forecast 24-hour accumulated rainfall” of moderate to heavy, which would trigger flooding, and landslides. Verification of the observed 24-hour accumulated rainfall values for Bicol area showed that the amount falls within the moderate to heavy categories, as forecasted.
2. For the segment “Weather Forecast” of the TV show “Failon Ngayon” aired on 12 January 2019, as follows:
In response, supplemental to the issuance of SWBs, the Southern Luzon PAGASA Regional Services Division (SLPRSD) at Legazpi City, Albay also issued separate color-coded Heavy Rainfall Warnings (HRWs) that covered hourly and 3-hourly rainfall forecast over Bicol Area. The first Heavy Rainfall Warning issued for TD Usman by SLPRSD was a Yellow Warning for Sorsogon at 2PM on 28 December 2018. Albay, where disastrous landslides occurred, was placed under Yellow Warning at 7PM on 28 December 2018. This was further elevated into an Orange Warning at 8PM and later a Red Warning at 11PM of the same day. These warnings, especially those of higher levels, are indicative of the need for “emergency” actions.
Based on available meteorological data at that time, TD Usman has weakened into a Low Pressure Area at landfall, which led to the lifting of Tropical Cyclone Warning Signal #1. However, this does not imply that weather will rapidly improve and the threat of flooding and landslides are immediately reduced. In the Final SWB issued at 8AM on 29 December 2018, PAGASA stated that moderate to heavy rains will continue over Bicol Region in the next 24 hours. This was reiterated in the Weather Advisory for LPA and Tail-end of Cold Front issued at 11AM of the same day.
Tropical Cyclone Warning Signal System, which has been in effect since 1930s, is based solely on expected winds and its impacts over a locality, and has no relation with the accompanying rainfall of such tropical cyclone (TC). However, PAGASA has always emphasized the threat of heavy rains and other hydrometeorological hazards and its impacts associated with each TC in it's HRWs and SWB.
PAGASA had ensured that warnings and pertinent information were disseminated to disaster managers at the national and local levels.
In addition to the regular issuances of SWBs and HRWs, among other warnings and information, during the Pre-Disaster Risk Assessment (PDRA) at the national and local level, PAGASA warned the DRRMOs/NDRRMC of prolonged heavy rainfall over areas to be affected by TD Usman, which could trigger flooding and landslides. It was also emphasized that rainfall over the past week made the soil very saturated, and even light to moderate rains could still trigger landslides in mountainous areas. Mines and Geoscience Bureau (MGB)had provided a list of areas with very high-high risk of floods and landslides during the PDRA.
The hardworking men and women of PAGASA remains committed to their mission of delivering reliable and relevant weather-related information, products and services to develop communities resilient to, among others, hydro-meteorological hazards during extreme weather events.
VICENTE B. MALANO, Ph.D.
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