WEATHERAmerica Newsletter, Saturday, September 27, 2008 at 6:45 P.M. CT

by LarryCosgrove | September 27, 2008 at 04:18 pm

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WEATHERAmerica Newsletter, Saturday, September 27, 2008 at 6:45 P.M. CT

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WEATHER HAZARDS (During The Next 24 Hours)

SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)
STRONG WINDS
(Hurricane Kyle)
E MA....Coastal NH....Downeast ME....NB....NS....PEI

ISOLATED Severe Thunderstorms
(Microbursts, Large Hail, Isolated Tornadoes)
E SD....MN....W ON

Some Thunderstorms May APPROACH Severe Limits
S FL

Some Thunderstorms May APPROACH Severe Limits
VA....DC....MD....DE....NJ....PA....NY

HEAVY RAINFALL OUTLOOK
(potential for an inch or more total rainfall within the next 24 hours)

Scattered Locations In
NY....CT....RI....MA....VT....NH....QB Eastern Townships....ME....NB....NS....PEI
(QPF 1 - 6")

Isolated Locations In
S FL
(QPF 1 - 2")

Isolated Locations In
N, C MB....W ON....MN....E SD
(QPF 1 - 2")

EXCESSIVE HEAT OUTLOOK
(potential for maximum temperature to exceed 95 deg F within the next 24 hours)

Scattered Locations In
CA....OR....S ID....NV....AZ....W NM....CO....W, C WY....UT

TROPICAL WEATHER SUMMARY
(review of disturbances over the Atlantic Basin and Eastern Equatorial Pacific Ocean)

Indian Ocean And The Orient

Typhoon Jangmi is nearing super typhoon status and should impact northern Taiwan within the next 12 to 24 hours. A huge surge, flood, and wind damage radius may devastate the area close to Taipei. Recurvature as a weakening tropical storm is expected on Sunday evening, with the remnant circulation and rainfall shield affecting much of Japan on Monday night and Tuesday.

Invest 98W is being affected by the outflow from Jangmi, but may attain depression status before making landfall in Vietnam during the next day or so.

Invest 99W is expected to become a tropical depression, then a named storm as the center moves slowly across the southwestern Pacific Basin over the following three days. The Philippines appear at greatest risk from this feature.

Eastern Equatorial Pacific Ocean

Impulses along the ITCZ are being sheared by low-latitude westerly flow aloft. There is some potential for tropical development, however, with impulses 800 miles south of Cabo San Lucas Mexico and another over eastern Panama.

Atlantic Basin

Hurricane Kyle is about 450 miles east of Cape Hatteras NC and moving due northward at about 15 mph. Kyle may briefly reach category 2 status before encountering cooler waters adjacent to the coastline of New England, New Brunswick and Nova Scotia. See the SHORT RANGE OUTLOOK below fir details on track and effects of Kyle.

A disturbed area over the Yucatan Peninsula and adjacent Caribbean Sea has some potential for development as it moves into the southernmost waters of the Gulf of Mexico. There is potential for significant rainfall and gusty winds from this features as it passes through southern Florida during the following 72 hours.

A closed 500MB low over the northern Gulf Stream is showing signs of acquiring a subtropical character. A westward drift is expected over the next two days before the low is picked up or otherwise nudged by a cold front moving through the northern Atlantic Ocean in the wake of Kyle.

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

Kyle Takes Aim At New England And The Maritime Provinces

Were it not for the huge 500MB cutoff low just south of the Grand Banks, Hurricane Kyle would have a relatively uneventful trip northeastward along the Gulf Stream before impacting the British Isles in about four days. But the gyre over the northern Atlantic Ocean is a reality, retrogressing and not allowing for a ridge in Newfoundland to give way. So with an element of blocking present, Kyle will likely continue to have more of a leftward bias to its track over the next 48 hours. It is still not out of the question that the west eyewall could scrape E MA as the center passes by on Sunday morning. More than likely the core of the Kyle circulation will make a final landfall in the vicinity of Downeast Maine, then accelerate through southern New Brunswick, clipping Prince Edward Island before becoming extratropical over the Gulf of St. Lawrence in the wee hours of Monday morning. Since Kyle may still be a nominal hurricane on its entry into the Maritime Provinces, issues with wind damage and heavy rainfall are to be expected. That said, Kyle is no Juan (landfall September 29 2003 at Halifax NS) and should not produce the devastating impacts seen with that system five years ago.

+PNA Ridge Complex Over Western U.S. Yields Warmth....

The Sonoran heat ridge is alive and well, and in fact may be a recurrent them through much of October over the Intermountain Region (giving way to the occasional cold front advancing out of the eastern Pacific Ocean). This subtropical high will keep the heat on in much of California, the Desert Regions and the lower Great Plains through the next three days. Remember, however, that this regime is very dry and will allow for nocturnal readings to drop sharply from daily maxima.

.....While Formative Trough Cools Down Locations East Of The Rocky Mountains

The persistence of the heat ridge will, in fact, produce very differing results to those living to the right of the axis of the anticyclone. Shortwaves will drop southeastward into the U.S. to the right of the Great Plains, carving out an impressive mean 500MB trough and allowing for frost/freeze producing temperatures to impact the Midwest and Northeast between September 30 and October 3. The cooler, drier regime will even reach, albeit in modified form, as far south as the Gulf Coast on Wednesday night and Thursday.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Impressive Cold Intrusion Forecast For The Midwest, Eastern Seaboard

It is highly unusual to get a deep, closed 500MB low into the lower Great Lakes in early October. So when you look at the attached graphic know that the jet stream configuration which is setting up over North America is NOT one which favors abundant warmth in the Midwest and Northeast. The cPk intrusion arriving on the last day of September will be transient, but in the process of moving eastward will reach well to the south, with the surface front passing through the Florida Straits and sending below normal thermal anomalies into the entire Gulf Coast region through late week.

Tropical Disturbance May Target Florida Peninsula

A recurring them in both the GFS and ECMWF model runs for some time now is for a stronger tropical system to form in the northwest Caribbean Sea at some point in the medium range. Despite the often divergent nature of the two equations and the respective ensemble families, these schemes predict the same scenario: that a disturbance rides along a frontal structure, recurves through Florida with torrential rainfall and some stronger wind fields before heading either along the Atlantic shoreline or taking a path out into the open waters of the ocean. As of now, the latter trajectory would seem to make the most sense, given the forecast width and strength of a building trough and cold intrusion across the eastern half of the U.S. in the 11 - 15 day time frame.

Impressive Gulf Of Alaska Low Likely To Chill Down The Pacific Northwest

In a pattern bearing eerie similarities to last fall, a procession of very strong storms is progressing across the northern Pacific Ocean. The second of two midlatitude cyclones, shown here east of the Kamchatka Peninsula, will reach the Gulf of Alaska in the medium range and begin to dislodge the powerful heat ridge ensconced across the Intermountain Region. The very cold temperatures associated with this gyre will effectively destroy the spell of warm to hot weather over the West, and may allow for early season snowfalls at higher elevations from BC, WA, and OR into the northern Rocky Mountains in about ten days. EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

-NAO, +PNA Signatures Loom Large In Longer Term Outlook

The numerical model suites have been in two different camps for nearly a week now. The ECMWF version and its variants insist on a trough West, ridge East configuration which, if it verified, would send very mild temperatures into most locations to the right of the Rocky Mountains. The GFS and GGEM schemes, however, have consistently maintained that any warming over the eastern states is transient, and show a persistent -NAO signature in the vicinity of southern Baffin Island and the Davis Strait. If this scenario verifies, temperatures would continue below normal, sometimes, greatly so, in much of the Midwest and Northeast heading into Mid-October.

Since the American and Canadian schemes have been (generally) more correct with the strength and destination of colder air over the past month, and since the most recent European model data now supports widespread cooling over the eastern half of the U.S. in the medium range, the call here is for a Rex signature to become established from N QB into southern Greenland with a Grand Banks vortex becoming established near NL. With an incoming cold intrusion, temperatures from the Great Plains into the Atlantic Coastal Plain look to be below normal during the extended period.

MTSAT Imagery Provides A Clue To Upcoming Trends Across North America

With a decidedly neutral ENSO configuration (albeit one showing a positive signature firmly in place over the 1,2 sectors), it makes sense to investigate the possibility of a colder temperature trend through the fall into the winter for areas east of the Rocky Mountains and below 40 N Latitude.You may recall that during the 2007-08 winter, linkage of strong shortwaves over the northern pacific Ocean with the equatorial regions was one of the main drivers in producing a volatile 500MB longwave pattern with frequent winter storms in the northern third of the U.S. This infusion of energy and moisture enabled frequent (if transient) building of -EPO and +PNA styled ridges, thereby enabling impressive intrusions of colder values into the Great Plains, Midwest, and interior Northeast. Satellite data shows some VERY intense disturbances moving along in the westerlies, which seem to be getting a boost of sorts from the flow which originates over the Indian Ocean and parts of Oceania. And with a -NAO signature apparent, it is not out of the question to say that parts of the Dixie and East Coast states could see a turn toward colder, stormier conditions in the weeks ahead.

Prepared by Meteorologist LARRY COSGROVE on
Saturday, September 27, 2008 at 6:45 P.M. CT

Disclaimer:

The previous statements are my opinions only, and should not be construed as definitive fact. Links provided on this newsletter are not affiliated with WEATHERAmerica and the publisher is not responsible for content posted or associated with those sites.

Copyright 2008 by Larry Cosgrove

All rights reserved.

This publication may not be reproduced or redistributed in whole or in part without the expressed written consent of the author.

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