‘Fujiwhara’ effect unlikely with ‘Rolly’ and ‘Atsani’ — PAGASA

Published October 30, 2020, 10:10 PM

by Alexandria Dennise San Juan

As back-to-back typhoons are threatening the country, the state weather bureau said on Friday that the two tropical cyclones are unlikely to interact with each other to cause a “Fujiwhara” effect.

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) is currently monitoring two weather disturbances — Typhoon “Rolly” which is moving near the country’s landmass, and Tropical Storm “Atsani” (international name) which is still outside the Philippine area of responsibility (PAR).

However, PAGASA said Atsani is expected to enter the country by Sunday or Monday — when Rolly is poised to make landfall over the Aurora-Quezon area.

PAGASA weather specialist Raymond Ordinario said that even if the two cyclones were both inside PAR this weekend, a dumbbell or Fujiwhara effect is still unlikely to happen as the center of the storms are far from each other.

“Malabo na magkaroon ng Fujiwhara effect kasi malayo ang sentro ng dalawang bagyo sa isa’t isa upang magkaroon ng direct interaction. (It is unlikely that there will be a Fujiwhara effect because the centers of the two storms are far from each other to have direct interaction),” Ordinario explained.

The Fujiwhara effect, as described by the US National Weather Service, is a phenomenon characterized by two storms orbiting each other, one moving in a counter-clockwise direction.

This happens when two cyclones spinning in the same direction pass close enough to each other and begin an intense “dance” around their common center. 

“Two storms closer in strength can gravitate towards each other until they reach a common point and merge, or merely spin each other around for a while before shooting off on their own paths,” it explained.

As of Friday afternoon, the eye of Rolly was spotted off 980 kilometers east of Casiguran, Aurora and continues to move west at 20 kilometers per hour.

Rolly further intensified and now packs a maximum sustained winds of 185 kilometers per hour near the center and gusts of up to 230 kilometers per hour.

Meanwhile, the center of Atsani was found 1,865 kilometers east of Visayas as of 4 p.m. Friday and has a maximum sustained winds of 65 kilometers per hour near the center and gusts of up to 80 kilometers per hour.

Atsani continues to move west-northwest at 35 kilometers per hour and is expected to enter PAR by Sunday or Monday where it will be locally named “Siony.”

PAGASA said Atsani will continue to intensify before entering the country and will likely develop into a severe tropical storm in the next 24 to 36 hours. 

However, Atsani is still less likely to bring severe weather over any portion of the country over the next three days, PAGASA added.

 
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