Tropical Cyclone Characteristics Associated with Extreme Precipitation in the Northern Philippines

Bernard Alan Racoma,Gerry Bagtasa,Nicholas Klingaman,Reinhard Schiemann,Christopher Holloway

doi:10.5194/egusphere-egu21-15486

Abstract

&lt;p&gt;The Philippines is exposed to Tropical Cyclones (TCs) throughout the year due to its location in the western North Pacific. While these TCs provide much-needed precipitation for the country&amp;#8217;s hydrological cycle, extreme precipitation from TCs may also cause damaging hazards such as floods and landslides. This study examines the relationship between TC extreme precipitation and TC characteristics, including movement speed, intensity, and season, for westward-moving TCs crossing Luzon, northern Philippines. We measure extreme precipitation by the Weighted Precipitation Exceedance (WPE), calculated against a 95&lt;sup&gt;th&lt;/sup&gt; percentile threshold, which considers both the magnitude and spatial extent of TC-related extreme precipitation.&lt;/p&gt;&lt;p&gt;WPE has a significant, moderate positive relationship with TC intensity and a significant, weak negative relationship with TC movement speed. When TCs are classified by pre-landfall intensity, Typhoons (1-minute maximum sustained wind speed &gt; 64 knots) tend to yield higher WPE than non-Typhoons (&lt; 64 knots). On the other hand, when TCs are classified by pre-landfall speed, Slow TCs (movement speed &lt; 11.38 knots) tend to yield higher WPE than Fast TCs (movement speed &gt; 11.38 knots). However, while distributions of WPE are similar between the Southwest Monsoon (June-September) and Northeast Monsoon (October-December) seasons, the relationship between pre-landfall TC intensity and WPE is more pronounced during June-September. These results suggest that it is important to consider the pre-landfall cyclone movement speed, intensity, and season to anticipate extreme precipitation of incoming TCs. A decision table considering these factors is devised to aid in TC extreme precipitation forecasting.&lt;/p&gt;

Highlights

The Philippines is in the southwestern portion of the western North Pacific (WNP) basin, the most active tropical cyclone (TC) basin
This study examines the relationship between TC extreme precipitation and TC characteristics, including movement speed, intensity and season, for westward-moving TCs crossing Luzon, northern Philippines
This study was motivated by the need to quantify the relationships between TC characteristics and TC precipitation

Summary

| INTRODUCTION

The Philippines is in the southwestern portion of the western North Pacific (WNP) basin, the most active tropical cyclone (TC) basin. This is done to create a TC dataset with similar paths upon landfall. As APHROuniform is derived from a daily precipitation dataset, it is possible there is a reduction of the signal of extreme precipitation by assuming a uniformly distributed precipitation throughout the 48-hr period Due to this limitation, the higher temporal resolution threehourly precipitation records of TRMM 3B42, version 7, hereafter TRMM3hr, were considered for this study. As the values of TRMM3hr on average are only 5% higher than TRMMuniform, we determined that assuming a uniformly distributed precipitation throughout the day for a daily dataset does not significantly reduce the signal for the occurrence of extreme precipitation. The areaweighted mean of all exceedances (including zeroes) is taken, and the calculated WPE for this TC is at 61.00 mm/2 days

| RESULTS

Findings

| DISCUSSION

| CONCLUSIONS