02W/PAKHAR Weakens To Tropical Storm, Threatens To Make Landfall In Viet Nam On Sunday

By:  Weatherguy Adonis

Adonis S. Manzan

 

Once Formidable Storm Weakens

Iloilo City, Philippines, 31 March 2012, (0400Z)–Category 1 Typhoon no more.  Our tropical system, “02W/PAKHAR” was a Typhoon no more as the winds died down gradually weakening its core, and the intensity readings went down to Tropical Storm threshold this morning.  Winds near its center was about 75 km/hr (40 kt) and gusting to 111 km/hr (60 kt), with central pressure of 998 hPa.  Tropical Storm “02W/PAKHAR” was located near 9.6N-109.9E or approximately 376.3 km South-southeast of Ho Chi Minh City, Viet Nam.  I am considering the Japan Meteorological Agency (JMA) scale measurement at the moment.

The Joint Typhoon Warning Center (JTWC) however pegged the system to be slightly stronger that of the JMA measurement at 111 km/hr (60 kt) with higher gusts reaching 140 km/hr (75 kt), making it a “Strong Tropical Storm,” almost at “Category 1 Typhoon” threshold by scale.

At the onset, the the prevailing “Upper level winds” are consistently favourable for the system to maintain its strength, despite the variation of existence of some drier air mass coming from its Southwestern periphery and a building Subtropical Ridge (STR) that should steer the system generally Westwards later tonight before making land fall along the coast of Viet Nam later tomorrow, 01 April 2012 at about nightfall according to some Numerical models that I have been checking out from time to time.

Fig. 1.0 "Typhoon 02W/PAKHAR lost its steam as convective banding tries to consolidate. A building STR should steer it towards Viet Nam coast sometime Sunday evening. Image Credit: CIRA."

Nevertheless, the oceanographic conditions are in aide for a slow but steady intensification phase of Tropical Storm “02W/PAKHAR” as it continues to stay offshore, away from land mass, but its outer bands have already arrived in advance since yesterday so flooding should not be a question anymore.

Meteorological Agencies Scale Up 02W/PAKHAR’s Intensity

There might be some confusion around here as regards to the Japan Meteorological Agency (JMA) definition of a “Tropical Storm” versus a full-pledge “Typhoon,” which the American models indicate, and in strong agreement with other interrelated Meteorological Agency across the Asia-Pacific Region.  By no means necessary, a “Tropical Storm” using the measurement scale of the Regional Specialized Meteorological Center (RSMC) based in Tokyo, Japan, under JMA’s operation, rap it up to between 62 km/hr (34 kt) and 88 km/hr (47 kt), and it all begins to come into mind that there are deep variations to this with that of a full-pledge “Typhoon,” that translates to a higher wind acceleration reaching above 118 km/hr (64 kt).

In the light of these, it clearly indicate a substantial difference with the interpretation of wind-average readings that uses a 10-minute wind average intervals.  The JMA uses this in terms of wind intensity sustained within the 10-minute period, as per World Meteorological Organization (WMO) regulation based in Geneva, Switzerland.

In most cases, this requirement are being observed by most of the weather agencies from around the world.  The 10-minute average we call it, points to a system that analyze the winds sustained within a Tropical Cyclone at a given time at a height of 10.0 m (33 ft), to which our state weather bureau, Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) also utilizes in reaching for a consensus in the event of a Tropical Cyclone threatening the Philippines within its Philippine Area of Responsibility” (PAR).

Fig. 2.0 "An impression I have made using the Vis Sat Imagery over the Western Pacific as shown, the weakened circulation along the East China Sea with evident convective banding that is occurring in aide of the system. To the far right, huge thunderstorms spawned by a passing Front pushes the La Niña-Easterlies well into Eastern Philippines. Image Credit: Digital-typhoon."

The Joint Typhoon Warning Center (JTWC) based in Pearl Harbour, Hawaii Island, USA uses another methodology, the “Saffir-Simpson Hurricane Scale,”  now this is anchored on the actual wind speed acceleration averaged over a 1-minute period, at 10 m (33 ft) above the ground.

Fig. 3.0 "MLSP readings indicate the confined vorticity remains offshore, and stronger gust constrained along the Southern edge of Tropical Storm 02W/PAKHAR at the moment. Image Credit: CIRA."

One’s failure to comprehend these variations add to the growing confusion which agencies of the two should prevail.  I hope putting up this issue now give due understanding of the difference between the readings, even I to date tend to miss some of this, frankly speaking!

Will Tropical Storm 02W/PAKHAR Again Intensify?

The answer is a resounding yes, considering the existence of low shearing environment and the favourable “Sea Surface Temperature” (SST) across the East China Sea.  I am not using the word, West Philippine Sea, or a.k.a. South China Sea because the matter now is beyond our territorial seas (Chuckle).

Since the system has reached its peak so to speak, in the meteorological aspect, we call it “Diurnal Maximum,” as indicated by the JTWC in its 2100Z bulletin, wherein a certain Tropical Cyclone has reached its peak intensity for a 24-hour period.  This refers also on the temperature that occurs after midday which maximum heat can be obtained in a considerable time, and vis-a-vis, the minimum before the Sun hits the horizon early in the morning.

In addition to this, the various factors could also be attributed to change in relative humidity at a given time, the clouds that feed and wrap around the convective towering cloud tops or the anvil thunderstorms that give these Tropical Cyclone a finite source of moisture and adequate amount of heat, equivalent to energy.

Fig. 4.0 "A NOAA eTrap indicate the rainfall totals within a 24-hr period as the system persists at East China Sea. Image Credit: NOAA."

Talk about energy, the Sun and the heat radiated from the surface of the Sea can also affect a storm’s life, and oh, before I forget, the precipitation or the rains that rise and fall within the clouds, it’s called “Condensation” and the rate of “Evaporation.”  These are all essential to a Tropical system.  The stages that undergone feeds into a system like a conveyor belt, which I believe it could have definitive impact on the “Atmospheric Pressure,” that can only be found inside the core of the Tropical Cyclone.

Fig. 5.0 "I made this impression I got from NASA Goddard Space Flight Center through Rob Gutro's article at NASA Hurricane Page. I give credit to the efforts made by NASA/SSAI, Hal Pierce. Thanks a million, guys!"

To what extent did our storm lose steam? We will find out later this afternoon if our discussion here of a gradual intensification phase holds water!  In the meantime,  I am signing off for more of these a bit later tonight.  Nonetheless, we’ll all keep a close eye on this one as it maintains its course, though stationary at times, it has been generating a lot of precipitation back here in the Philippines for quite some time now.

Also, my fellow “Kababayans” in flood-ravaged towns of Mindoro Occidental, Bicol Region and parts of Capiz nearest to my location should take a look into the upcoming thunderheads that hover above us.  Right now I have been observing large thunderstorm anvils shooting into the atmosphere sending rumbling thunder ahead of the thunderstorms that could come at any moment soon!

This has been your Weatherguy hailing from the Philippines, Mabuhay! =)

With data from NOAA, NASA, CIRA, JTWC, JMA, HKO, NRL Mry and Typhoon2000.ph

(Note: If you have queries, email me at amanzan@smartbro.net or through–>weatherguyadonis@theboplive.net)

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About Weatherguy Adonis

"All worked up for the study of meteorology whenever, wherever across the world. You name it, I have some of it! LOL!" ;D

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