2013 WPAC Season

[dexterlabio]

TSR lowered their numbers and now anticipates below normal activity. Seems reasonable given the dud the start of the season, with Soulik being the only storm who made most of the ACE so far.

[Typhoon Hunter]

Well we're actually above average when it comes to numbers so that would make this a busy season so far...? Of course not, ACE is around 40% of what it should be and the season is really struggling. This is exactly when I regard ACE as a much more useful quantifier than number of storms. Wpac really mimicking the Atlantic last year!

[dexterlabio]

Well not exactly because we had a Category 4 system, last year the atlantic had a 100-knot Category 3's at most...

Below average season doesn't always mean no intense or interesting systems... 1998 is a good example.

[Typhoon Hunter]

Soulik could have been a cat 5 and we'd still be facing the same situation. A ratio of 10 storms to 1 typhoon is not usual so something strange has / is going on. I find this more strange than a traditional slow season with few storms and thus a lower ACE.

I'm not saying this will continue for the rest of the season, who knows what will happen, but the trend so far is similar to the problems the Atlantic faced last year.

[Hurricane Alexis]

Soulik could have been a cat 5 and we'd still be facing the same situation. A ratio of 10 storms to 1 typhoon is not usual so something strange has / is going on. I find this more strange than a traditional slow season with few storms and thus a lower ACE.

I'm not saying this will continue for the rest of the season, who knows what will happen, but the trend so far is similar to the problems the Atlantic faced last year.

Just curious. What exactly is a slow season in the wpac?

[RobWESTPACWX]

On average by this time we have over 3-5 Typhoons. July alone averages about 3. With just 1 it really is a slow year. A lot of odd stuff going on though. The westpac high is just suppressing anything from pushing north at this time and keeping Okinawa and Central China baking.

Although we have had back to back weaker monsoonal type storms developing in the Philippine area. But those really have not shown Typhoon potential.

[Typhoon Hunter]

Just curious. What exactly is a slow season in the wpac?

Named storm average is around 26 per year and ACE is around 300 using JTWC figures.

[dexterlabio]

Could the dominant westpac high be the reason why this season has been slow so far?

[Typhoon Hunter]

Could the dominant westpac high be the reason why this season has been slow so far?

That's what I'm curious about too Dexter. It's been very strong and might account for the lack of storm formation east of 130E.

[mrbagyo]

Could the dominant westpac high be the reason why this season has been slow so far?

That's what I'm curious about too Dexter. It's been very strong and might account for the lack of storm formation east of 130E.

yeah I think it has an effect,,, that high pressure area is unusually strong, and it's position - that should be the position of the STR in the "BER" months...
JMA also showed that it's been stationary for too long... I think it's causing every system to move westward fairly rapidly.
Look at Soulik, look at the mini swirl, look at the past invests in WPAC. they can't establish themselves while they were under that strong STR... actually the South china Sea is more active than the main basin... and take note of the lack of RECURVING STORMS??? most are west tracker...... what's happening???

[dexterlabio]

^yeah if you look at the steering layer maps right now, you can compare it with the steering pattern during Nov-Dec and you won't see much difference.

This setup occurs usually during La Nina years..also during these years when tropical cyclone activity is suppressed east of 130E. And again, let me cite years 1998 and 2010 as examples. Haha I know I've been raising this point for too long now. But, maybe cold neutral has the same effect as La Nina in this basin?

[cycloneye]

The basin continues very active right with developing 11W and new Invest 97W.

[dexterlabio]

So we finally have the first supertyphoon of the season, and officially the strongest typhoon of the season so far.

Meanwhile, recent GFS runs caught my attention as it's showing something 'tropical' developing near Taiwan later this week. Is that a tropical cyclone or non-tropical in nature? I've never seen something like that, even in model outputs...

[mrbagyo]

I just saw the latest run from GFS and it's indeed showing a development near Taiwan and it also appears to be a strong one ... I just don't get the southward movement... influence of deep Subtropical ridge again???

NAVGEM and CMC also develop that system near Taiwan...with CMC going "ballistic" as usual... GFS also shows a system from CPac to develop here in WPAC in the long range...
Interesting...

[dexterlabio]

That southward motion gives me the impresiion that it is subtropical, I also thought cyclones forming near that latitude are rare...

[vrif]

This is my analysis on why it moves south from the 12Z GFS. If there is anything wrong with my analysis feel free to correct me!

Between +0 and +24, southeast winds blow towards Taiwan due to TY Utor's circulation. This causes a lee vortex to form in the northern portion of the Taiwan Strait which forces winds to move down the Taiwan Strait causing a convergence line with winds from the southeast(orange arrows). Also an outer band from Utor (solid black line) is moving northwards towards the convergence area, which aids in upward vertical movement of air.



On the 200 hPa analysis for +24. The outer band causes a jet streak (orange arrow) which creates a favourable upward region to its south west (red box).



Looking at the +36 MLSP, the red circle indicates the convergence area swirling in the Taiwan Strait. The background wind flow is from the southwest but looking at the 925 hPa (dashed line) it cannot progress further north due to high pressures blocking its progression. Therefore it is forced to move east or south from its location. When it moves back out to the Pacific Ocean, there is still an upper level divergence area formed from the same outer band jet streak. This helps with further intensification.



Also at +36, a trough is pushing down from the north, causing this system to be pushed to the south. The tail end of the trough will be cut off, creating an upper low stationed just south of Shanghai in the later forecast hours.

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[euro6208]

During Week-1, tropical cyclone (TC) formation chances remain elevated for parts of the West Pacific, mainly north of 20N. The greatest threat is just east of Taiwan, while lower probabilities of TC formation are forecast just to the east of that region where a second vorticity center could develop into a tropical storm.

[mrbagyo]

91C is moving closer to the dateline...

[Hurricane_Luis]

91C is moving closer to the dateline...

Looks like it will move across the dateline as a named storm.

CP, 01, 2013081612, , BEST, 0, 100N, 1730W, 35, 1005, TS,

[mrbagyo]

91C is moving closer to the dateline...

Looks like it will move across the dateline as a named storm.

CP, 01, 2013081612, , BEST, 0, 100N, 1730W, 35, 1005, TS,

yeah. it's now a named storm.. tropical storm PEWA