WPAC: MEGI (1013/15W) - Tropical Depression

[ricmood]

moving sw directly hitting metro manila???

[euro6208]

My family is from Sumabnit Binalonan

What is the highest T number that Megi reached? I saw on some websites that Megi reach 7.5

[supercane]

Anyone know, based on past storm tracks across Luzon, if the terrain might affect the storm's path any like Fanapi did with Taiwan's coast?

Yes, orographics (mountains) can have an effect on storm motion. As most meteorology questions, the answer is complicated. Two studies are presented.

1) Brand, Samson, Jack W. Blelloch, 1973: Changes in the Characteristics of Typhoons Crossing the Philippines. J. Appl. Meteor., 12, 104–109. Links to Abstract | PDF

Abstract
Thirty typhoons (1960–70) are examined to determine the effect of the Philippines an the intensity, speed of movement, and size characteristics of tropical cyclones crossing the Philippines. The results show an average intensity (maximum surface wind) decrease of 33%, a northward perturbation as the storms pass through the Islands, and a decrease of circulation size for weak typhoons. The study also showed an increase in speed of movement as storms approach the Philippines.

2) Bender, Morris A., Robert E. Tuleya, Yoshio Kurihara, 1987: A Numerical Study of the Effect of Island Terrain on Tropical Cyclones. [cite]Mon. Wea. Rev.[/cite], 115, 130–155. Links to Abstract | PDF

Abstract
A triply nested, movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges. The integration domain consisted of a 37° wide and 45° long channel, with an innermost mesh resolution of 1/6°. The storms used for this study were embedded in easterly flows of 5 and 10 m s−1 initially. Realistic distributions of island topography at 1/6° resolution were inserted into the model domain for the region of the Caribbean, including the islands of Cuba, Hispaniola, and Puerto Rico; the island of Taiwan; and the region of Luzon in the northern Philippines.

It was found that the islands affected the basic flow as well as the wind field directly associated with the storm system. The combination of these effects caused changes in the track and translational speed of the storm. In particular, in the case of the 5 m s−1 easterly flow, the storm accelerated and veered to the north well before reaching Taiwan. For the other island distributions, the northward deflection of the track and the increase of translational speed occurred near and over the islands. After landfall, the surface pressure underwent rapid filling. As the tropical cyclone passed over Hispaniola, the surface low continued to move along with the upper level vortex as it transversed the mountain range, while over Luzon it became obscure before reforming on the lee side slope of the mountain. In case of Taiwan and the 10 m s−1 easterly zonal flow, secondary surface lows developed behind the mountain range. The upper level vortex in this case became detached from the original surface low and eventually coupled with a secondary one.

The intensity changes of the storm near and over the islands were strongly related to the latent energy supply and the vertical coherence of the storm system. Advection of dry air from near or above the mountain tops into the storm area caused significant weakening of all the storms moving with the weaker easterly flow. Storms leaving Hispaniola and moving over open sea quickly reintensified as their vertical structure remained coherent. On the other hand, storms leaving Luzon were disorganized and did not reintensify until several hours later when the vertical coherence of the systems was reestablished.

Although these experiments were performed for an idealized experimental design and basic flow, many observed storms have exhibited similar behavior in track deviation and decay. This implies that the effect of detailed topography should be considered if an accurate forecast of the storm direction and behavior is to be made.

----------------

What to take away from these studies in the case of Megi? A drop in intensity is a no-brainer. The first study states that intense storms (those with MSW >90 kt) can decrease in intensity by as much as ~50%, and the second study states that recovery of intensity is slow and takes some time (ie several hundred kilometers) as the centers at various levels regain vertical coherence. As for movement, I think that the large-scale motion around the subtropical ridge (STR) will prevail; however, as the second study shows with the numerical model simulation, a slight leftward bend and acceleration prior to landfall and then a north-of-track movement through the island would be a stereotypic response to the mountains.

Complicated, I know. Hope this helps.

[ManilaTC]

Intensity Very Intense
Center position N18°40'(18.7°)
E126°50'(126.8°)
Direction and speed of movement W 20km/h(12kt)
Central pressure 910hPa
Maximum wind speed near the center 60m/s(115kt)
Maximum wind gust speed 85m/s(165kt)
Area of 50kt winds or more Wide 200km(110NM)
Area of 30kt winds or more E410km(220NM)
W330km(180NM)

[Aslkahuna]

Anyone know, based on past storm tracks across Luzon, if the terrain might affect the storm's path any like Fanapi did with Taiwan's coast? I'd never seen anything like it, but then again, I haven't been tracking very long. Then again, this is a big Cat 5, not a relatively small (size-wise, not intensity-wise) Cat 3...maybe this bad boy doesn't care what's standing in its' path! I'm just a little worried with my husband there. This moves a little to the south and it's going to be bad news for him. He sent me some photos he took from the air of Luzon - looked pretty moutainous.

probably nothing too significant of a shift imo... mountains in central northern luzon are usually around 1500-2500m (Mt Pulag being the highest at 2922m)... it will surely weaken but i don't think it will change "Megi's" track.. i mean, we have the Sierra Madre mountain ranges on the Eastern part of Luzon, and as far as i know it only weakens typhoons, i haven't seen any erratic track from storms that have passed through in that region...

of course, i might be wrong...

Actually, when tracking storms in the 1970's with the radar at Clark I did notice from time to time shifts in the tracks caused by the terrain-it depended upon storm size since smaller wound up storms tended to shift more than the big monsters that were much bigger than Luzon itself. One important terrain effect was how a leeside low would develop along the West Coast of Luzon and sit in place until the mid level circulation came over at which point it became the new LLCC and began intensifying. This would have an impact upon the wind patterns at Clark

Steve

[euro6208]

May God bless everyone in the Philippines.

[supercane]

WTPQ20 RJTD 170600
RSMC TROPICAL CYCLONE ADVISORY
NAME TY 1013 MEGI (1013)
ANALYSIS
PSTN 170600UTC 18.5N 126.2E GOOD
MOVE W 12KT
PRES 910HPA
MXWD 115KT
GUST 165KT
50KT 110NM
30KT 270NM EAST 220NM WEST
FORECAST
24HF 180600UTC 18.0N 121.5E 75NM 70%
MOVE W 11KT
PRES 950HPA
MXWD 080KT
GUST 115KT
48HF 190600UTC 17.1N 117.6E 110NM 70%
MOVE W 10KT
PRES 945HPA
MXWD 085KT
GUST 120KT
72HF 200600UTC 17.3N 115.8E 160NM 70%
MOVE W SLOWLY
PRES 940HPA
MXWD 085KT
GUST 120KT =


WTPQ20 BABJ 170600
SUBJECTIVE FORECAST
SuperTY MEGI 1013 (1013) INITIAL TIME 170600 UTC
00HR 18.6N 126.2E 910HPA 65M/S
30KTS 300KM
50KTS 100KM
P12HR W 25KM/H
P+24HR 18.2N 121.3E 940HPA 50M/S
P+48HR 17.8N 118.2E 950HPA 45M/S
P+72HR 18.0N 116.1E 945HPA 48M/S
P+96HR 18.6N 114.7E 930HPA 52M/S
P+120HR 19.4N 113.4E 930HPA 52M/S=

[supercane]

My family is from Sumabnit Binalonan

What is the highest T number that Megi reached? I saw on some websites that Megi reach 7.5

As with everything regarding intensity, there is one number. In the Western Pacific, estimates from RJTD (JMA, Japan Meteorological Agency), PGTW (USA's Joint Typhoon Warning Center), and KNES (also USA Satellite Service Branch) provide estimates of storm intensity via satellite estimates using the Dvorak technique. As far as I've seen today, the peak T number from all 3 agencies was T7.0. CIMSS from the Univ. of Wisconsin also provides an experimental Advanced Dvorak Technique estimate that more quickly responds to rapidly intensifying storms, although in my experience it also tends to run high. In Megi's case, its frequent updates accurately tracked the storms rapid intensification better than the 6 hourly updates from the above agencies. You may have seen raw T numbers above 7.0 there.

Hope this helps, and stay safe.

[phwxenthusiast]

Actually, when tracking storms in the 1970's with the radar at Clark I did notice from time to time shifts in the tracks caused by the terrain-it depended upon storm size since smaller wound up storms tended to shift more than the big monsters that were much bigger than Luzon itself. One important terrain effect was how a leeside low would develop along the West Coast of Luzon and sit in place until the mid level circulation came over at which point it became the new LLCC and began intensifying. This would have an impact upon the wind patterns at Clark

Steve

thank you for your input...

i guess it's just nowcasting time you know...?? good thing PAGASA is issuing hourly updates now.. but for people who don't have power (which i think include majority of N. Luzon), they just have to weather the storm i guess... just hope for the best

[supercane]

WTPQ50 RJTD 170600
RSMC TROPICAL CYCLONE ADVISORY
NAME TY 1013 MEGI (1013)
ANALYSIS
PSTN 170600UTC 18.5N 126.2E GOOD
MOVE W 12KT
PRES 910HPA
MXWD 115KT
GUST 165KT
50KT 110NM
30KT 270NM EAST 220NM WEST
FORECAST
24HF 180600UTC 18.0N 121.5E 75NM 70%
MOVE W 11KT
PRES 950HPA
MXWD 080KT
GUST 115KT
48HF 190600UTC 17.1N 117.6E 110NM 70%
MOVE W 10KT
PRES 945HPA
MXWD 085KT
GUST 120KT
72HF 200600UTC 17.3N 115.8E 160NM 70%
MOVE W SLOWLY
PRES 940HPA
MXWD 085KT
GUST 120KT
96HF 210600UTC 17.8N 114.9E 200NM 70%
MOVE ALMOST STATIONARY
120HF 220600UTC 18.8N 114.6E 260NM 70%
MOVE NNW SLOWLY =

[Typhoon10]

The latest post by supercane shows as swing to the north once in the SCS. Do we think thats accurate and possible? Should us here in HK start to get concerned?

[supercane]

[quot]
Yes! When people here that "super typhoon" it's like saying in the states a Cat 5 is headed towards you, people listen and they go O, this is going to be really bad. I think that would be safe. Also I think Pagasa should start increasing there signal force. A little early but I think it would be ok for Aparri and Santa Ana.

another thing i don't like with PAGASA... signal no 3 is only issued 18hrs prior to the storm landfall... that doesn't give you much time to prepare does it??[/quot]

I would like to see PAGASA use a system like the NWS does, with watches and warnings. That would be more effective in preventing casualties. Sometimes by the time they issue signal 4 the storm's already too close.

PAGASA are up to 105 knots/938 hPa but are still way off.

i want to see that too... much simpler and doesn't have the technicality of having different signal warnings for different intensities... furthermore, do you know that the cancellation of classes is based on the signal warnings issued by PAGASA??
signal 1 no classes in elementary, 2 no classes up to high school, 3 no classes in college... it's really messed up; do they expect college students to weather out signal 2 winds and heavy rain?!?!

@rob... exactly... there has to be some kind of major revamp in PAGASA, not only in personnel but also on their forecasting as a whole... no amount of state of the art equipments can help them if they keep sticking to the "old system" that they have...

maybe you can work for them once they modernize... lol

[soapbox]
I wanted to address this earlier but was too busy with the recon reports. This is not directed toward any one person, but I am concerned about the tone taken by some in posts regarding PAGASA. I don't think anyone would say that PAGASA is among the more sophisticated warning agencies in the Western Pacific basin. However, unless someone can prove otherwise, I have no reason to think that they are lazy, uneducated, or less dedicated to their job than other meteorologists. The fact is that the Philippines is still relatively poor economically compared to its other neighbors, and that those budgetary restraints reflect themselves in poor facilities and equipment, so much so that other countries like Japan must offer grants to upgrade the country's radar net. Like American schoolteachers, meteorologists do not want to work in such conditions, and as a result there is a meteorologist "brain drain" of talented scientists away from the Philippines and to more prosperous countries, as this article shows. While the regional Typhoon Committee does offer technical assistance in terms of computer models and professional development, such help cannot erase all the problems PAGASA faces overnight.

As for meteorological facts, many bemoaned that PAGASA was slow in upping its wind estimates. Although I agree, when you compare it to HKO, the wind speed estimates provided by the two are not too different.
PAGASA
11pm-140 km/h
5 am-160 km/h
11 am-195 km/h
HKO
8pm-195 km/h
8am-155 km/h
And while PAGASA's pressure estimate may be high, they are not the only agency guilty of ignoring recon data in this quite rare situation.

Neither a watch/warning paradigm (US) or a storm signal paradigm (PAGASA, HKO, etc.) is necessarily better than the other; it all depends on how good the warning dissemination system is. I assume HKO does well enough with its storm signals. I agree that longer lead times and possible simplifications are worthy goals.

I also think that the hourly update initiative is a sign of promising too much in the face of public pressure. Even the NHC only provides hourly updates when a storm is in US radar range. For PAGASA's limited staff, the advantage of positive PR may be offset by less attention to incoming storms.

Storm2K traditionally has a no-bash policy regarding the NHC, and while I think it may be enforced somewhat strongly by the moderators, I do believe in its basic intent and that the policy should be extended to other warning agencies worldwide (i.e., bash the decision, not the agency or forecaster). I understand the frustration with PAGASA's products and think that PAGASA can and should do better, but there's a fine line between constructive criticism and needless invection.
[/soapbox]

[Typhoon Hunter]

Going live on CNN International at 1000GMT / 1800HK and Philippines time.

[dexterlabio]

^You have a point there. Just more like hating the sin, not the sinner (I'm not saying that PAGASA is making any sin though ). The more I bash "outrageous" forecast, the more I pity their situation, because their government carries a lot of burden and it cannot focus on the improvement of the weather agency alone. As much as I get baffled, I try my best to understand what they've been going through.


Back to Megi, it's still maintaining that well-defined eye. Rainbands have reached Northern Luzon.

[dexterlabio]

Going live on CNN International at 1000GMT / 1800HK and Philippines time.

I'm excited for your mission in Megi. God bless and stay safe!

[Chacor]

Thanks for the update James, will watch for it. Good luck with this. Looks like Hong Kong will need to be ready if that turn pans out. JTWC and JMA in agreement on recurving now.

[P.K.]

Does anyone know why some agencies are not using the central pressure found by the RECON?

Well, this may sound ignorant and kind of silly, but ever think that maybe some of the agencies can't read the recon or how to get the site with the recon since it's in english? Just food for thought....

I was wondering about this before. Given how rare recon is we don't know how much training, if any, they have in reading recon obs. We are all comfortable using them here but then we read them all the time from the NHC.

[Typhoon Hunter]

Cheers guys, appreciate the comments.

It looks like we'll say in Aparri even if the storm tracks a little to the south. That way we'll be able to document any damage and aftermath on our travel back to Tuguegarao.

[RobWESTPACWX]

Going live on CNN International at 1000GMT / 1800HK and Philippines time.

Have it on waiting for you! CNN JP though, I hope your on that.

[dexterlabio]

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