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    Rain in Karachi; Western Pacific Lighting Up

    July 26, 2011, 9:59:56 AM EDT

    FIRST MEASURABLE RAIN OF THE SEASON

    I do not know how much rain has fallen as of yet (I should be able to know soon), but the weather observations out of Karachi, Pakistan, show downpours with late-day thunderstorms on Tuesday, July 26. The last measurable rain at this site happened last winter on Feb. 20.

    Last year, there had already been no fewer than two substantial falls of rain at the same site.

    The trigger for the thunderstorms in Karachi and elsewhere in Sindh seems to have been a low pressure wave riding the easterly jet stream (a normal aspect of mid-summer weather maps of the Subcontinent) westward over Gujarat to the northern Arabian Sea. This should have tapped moisture in the low-level Monsoon southwesterlies.

    As for the thunderstorms that wetted Pakistan, these seem to have shifted westward over southwestern Pakistan in the region of Baluchistan.

    The bigger picture for the Subcontinent seems to be that the west-bound wave temporarily lowered rain coverage in its wake over most of India during the last few days.

    As the wave leaves the area by way of Oman (where it will spark stray thunderstorms Wednesday), the some rise in rain coverage and intensity should happen during the next few days in the Subcontinent as a whole. The should include heavy falls against the west coast and western slopes. Sindh, on the other hand, will see fewer storms Wednesday and thereafter.

    TWO TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC OCEAN

    Tropical Storm Nock-Ten (10W) is crossing Philippines even as I write. This moderate tropical storm has been a big rainmaker in east-central Philippines (Catanduanes and southeastern Luzon). Rainfall has been in the neighborhood of 48 cm, or 19 inches, at Virac (Catanduanes) and Legaspi (Luzon).

    A trek towards the west-northwest, across central Luzon (and greater Manila), will be followed by a return to sea by Thursday. Nock-Ten will leave further flooding rain in its wake.

    Next land in the path of Nock-Ten will be southernmost China, likely Hainan, and northern Vietnam. Whether or not it becomes a typhoon, I do not know. The Joint Typhoon Warning Center (JTWC) say no.

    My recollection is that mid-summer cyclones over the South China Sea tend to buck unfavorable northerly shearing winds aloft, and often have top winds held below typhoon status.

    JAPAN WILL BE WATCHING TD 11W

    Tropical Depression Eleven (11W) will be the next tropical storm, maybe even the next typhoon. TD 11W is south-southwest of Guam, aimed towards the northwest.

    The JTWC forecast 11W to gain typhoon status over the open Philippine Sea on Friday (late-day, local time).

    Ultimately, 11W could reach the shores of Japan, although this would not happen until sometime next week.

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