--This is no news flash to anyone following the story of a would-be Arabian Sea cyclone. It became clear late last week that this was not going to happen. It took some time for the foremost cause of this none-happening to show. The culprit? A "Western Disturbance," which is another name for a short-wave trough in the westerlies. Anyways, this western disturbance was not indicated at the time that numerical forecast were showing a tropical cyclone (low) off western India., which is consistent inasmuch as the northern system (of the strength it happened to be) would be expected to preclude a tropical cyclone over the northern Arabian Sea.
The western disturbance that blocked any Arabian Sea cyclone dipped out of Afghanistan and into Pakistan during the weekend. In so doing, it set up southerly steering wind flow over much of the Subcontinent. Enter a tropical wave drifting west from the Bay of Bengal. The shift to southerly steering winds veering this wave northward along a path to the east of the Western Ghats.
Ironically, the western disturbance was the spark for rain in Pakistan rather than any tropical low, but the rain happened far to the north as thunderstorms along the northern edge of the plains. As had been forecast, offshore wind flow and blazing sun put Karachi on the "hot plate" with four-straight, 100-degree days. Hottest were Friday (107 F/41.8 C) and Saturday (106 F/40 C).
-Rain-wise, India did well by this tropical weather system. Indeed, "too well" in areas of Karnataka that were swept by major flooding unleashed by its rain. There was an unbroken swath of heavy to very heavy rain across the mid-south of India, especially over Andhra Pradesh and Karnataka into Maharshtra. Kurnool, Andhra, was hit hard.
Now, with the tropical wave winging northward for the Himalaya, Mumbai has picked up 16 cm of rain within 48 hours. All of October has had, on average, only about 6 cm. Also doused during the last few days have been areas of Madhya and Uttar (14 cm at Agra).
-Looking forward, the word for the Subcontinent is that "it is not over" -- yet. The tropical wave is slowly tracking towards the north and the northeast. The steamy tropical settle that surrounds the wave (still a part of the SW Monsoon, I would say) will help to instigate further local heavy to very heavy falls between north-central India and the middle and eastern foothills. The last of the heavy rain will fall along the eastern foothills late in the week.
(NRLMRY image)
--Typhoon Parma struck storm-weary Luzon Island late last week. Landfall was over the northeast, where wind damage was severe. However, I believe that highest rainfall has happened over the northwest of the island: Laoag City, Vigan and even as far south as the highland city of Baguio. Best that I can tell, based upon our database here at AccuWeather.com, rainfall has topped 80 cm at Laoag with nearly 70 cm pelting Vigan. Both Vigan and Baguio claimed 50-cm falls of rain during their respective wettest 24-hour spans.
-Trouble with Parma (as of 1800 UTC, Monday, a strong tropical storm roughly between Luzon and Taiwan) is that it is stuck in a region of light steering winds. Which means that it will spin for a few days off northern Luzon (or maybe southern Taiwan) unleashing even more extremely heavy rainfall. It was a typhoon last summer that unloaded about 2.5 meters of rain upon some highland site in Taiwan. Parma could potentially double the rain amounts already received over northwestern Luzon.
(JTWC image)
--Melor has been a dramatic super typhoon over the open Philippine Sea following its crossing of the Mariana Islands late last week. Anatahan, the whole island a volcano, took a direct hit from Melor.
-Melor will veer northward and northeastward east of the Ryukyu Islands (Okinawa among them) on Tuesday and Wednesday. It will then track over, or barely south of, the southern Japan mainland on late Wednesday to Thursday. Looks as though it will still be a typhoon, albeit a weakening one. This also looks like a potentially devastating storm wielding torrential, flooding rain and destructive wind. A cold front settling southward into the path of the typhoon will work to shunt its path eastwards while also greatly bolstering rainfall to its north.
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Dear Mr. Jim,
will you foresee the prospects of setting in of north east monsoon by october 10th to oct12th.
chennai has become very hotter for the past one week, the maximum hovering around 37 C.
your views please.
suresh
Reply:
Dear Suresh,
No sweeping shifts in sight. I do see weakening of the SW Monsoon over Tamil after Oct 10, so the heat should lessen somewhat. At the same time, nothing that looks to me like a true NE Monsoon at this time.
Jim
Posted by ssuresh | October 7, 2009 10:37 AM
Dear jim:Daily Heavy rain in mumbai,goa,pune and some areas of gujrat also but no name of rain/clouds over karachi.why?
Reply:
Dear Shoaib,
As I see it, the key to the path of rain keeping far to the east of Karachi was the "Western Disturbance" that dipped southeast by way of Afghanistan. Westerly steering winds coincident with the WD shunted the rain-bearing flow east of Pakistan.
Jim
Posted by shoaib | October 6, 2009 11:27 AM
I made a mistake in my last comment, I meant the rain that fell on Monday and Tuesday morning was heavy, not Wednesday and Thursday that havent arrived yet!! lol & sorry!
Posted by Amir | October 6, 2009 4:22 AM
Dear Jim
Surprise for us! really heavy downpours here in Pune made all of us happy after a semi-dry monsoon.
Again I dont have the numbers, but the rain that fell Wednesday and Thursday morning local time was really heavy, hard and long lasting, not like any October passing shower. you were talking about the continue of rain in some parts, do you think Pune and Maharashtra will get more as well?
Regards
Dear Amir,
The site of record at Pune had 66 mm split into two outbursts happening on consecutive days. Last of these was on Monday eve. Our data show normal October monthly rainfall of 92 mm, so you are nearly 3/4 of the way there.
Looking forward, southward settling of the Westerlies into the Subcontinent will bring dry air southward to at least the northwestern Deccan (and Pune). I do not foreseen any rainy outbreaks at this time.
Jim
Posted by Amir | October 6, 2009 4:20 AM
Hi Jim, i was the most happy man when on 1st oct accuweather predicted around 366mm of rain on 2nd,3rd, 4th and 5th oct. Suddenly it came to 26mm and finally what we got a measly 11mm on sunday and that was all,what a big let down after such a hype i guess thats what they call the weather blues.The interaction of the westerlies which you said stopped the formation of the cyclone in the arabian sea and the tropical wave from the bay i was really looking forward for the heavy rains as the heat was unbearable.Jim what was the cause did the system did not have the punch to penetrate in our region or the wind shear kindly put in some words to make me understand what went wrong ? regards,Anuj Arora from Chandigarh, INDIA
Reply:
Dear Anuj,
Well, I cannot cite any one factor as that keeping rains to your east. The Western Disturbance proved to be far stronger than anything forecast along with the earlier cyclone scenario. Much stronger WD kept the Bay tropical wave (together with its deep tropical moisture and swathe of rain) on a more easterly track. Moreover, the more easterly path precluded the consolidation of a well-marked monsoon low, much less an Arabian Sea tropical cyclone.
In short, the forecast scenarios showing tropical cyclone together with abnormal heavy rain far to the west and north were calling for something that is rare, indeed. This is why skilled forecasters need to interpret the output of numerical (computer) forecast models, which is no more than simulations of atmospheric conditions over time.
Jim
Posted by Anuj Arora | October 5, 2009 11:27 PM
likewise, enjoy your work. I find your prose styling much more engaging than the bland wire reports.
being in Kansai, i'll be keeping track of Melor here..
Posted by robert | October 5, 2009 10:28 PM
H1 Jim,
Your blog is very informative. I love it...
Did you see the floods in South India ? Apparently, millions have been left homeless....
Reply,
Dear Jaswanth,
Thank you for the kind words.
Yes, I was aware that serious flooding and disruption were under way, the states of Karnataka and Andhra Pradesh being oft-cited in the new stories. In light of the observed rainfall (as it has come to my awareness through our database), I am somewhat struck by the severity of the flooding. Falls of rain will doubtless a good deal higher away from the sites for which we have information.
Jim
Posted by Jaswanth | October 5, 2009 8:07 PM