WEATHERAmerica Newsletter, Saturday, September 6, 2008 at 5:55 P.M. CT

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WEATHERAmerica Newsletter, Saturday, September 6, 2008 at 5:55 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
(Tropical Storm Hanna)
N NJ....NE PA....S NY....CT....RI....MA....S VT....S NH....C, S ME....E NB....NS
PEI....S NL (NWF Island)

ISOLATED Severe Thunderstorms
(Microbursts, Large Hail)
SE ON....Lower MI....N IN....N OH....W NY

ISOLATED Severe Thunderstorms
(Microbursts, Large Hail, Isolated Tornadoes)
AB.....W, C MT....N WY....SW SD....N NE....N IA....MN....W IA....Upper MI....W ON
MB....SK

Some Thunderstorms May APPROACH Severe Limits
Coastal LA, MS, AL....FL Panhandle....S GA....Coastal SC

Some Thunderstorms May APPROACH Severe Limits
NM


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

Scattered Locations In
N NJ....NE PA....S NY....CT....RI....MA....S VT....S NH....C, S ME....E NB....NS
PEI....S NL (NWF Island)
(QPF 1 - 6")

Scattered Locations In
SE ON....Lower MI....N IN....N OH....W NY
(QPF 1 - 2")

Isolated Locations In
AB.....W, C MT....N WY....SW SD....N NE....N IA....MN....W IA....Upper MI....W ON
MB....SK
(QPF 1 - 2")

Isolated Locations In
NM
(QPF 1 - 2")


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

Scattered Locations In
S OR....CA....NV....AZ....UT....CO....NM....TX....OK....S AR....LA....MS....AL....FL
GA....SC....NC....extreme S VA

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

Eastern Equatorial Pacific Ocean

Invest 99 about 400 miles south of Cabo San Lucas Mexico; may soon become a tropical depression with north to northeast motion toward the Mexican mainland.

Atlantic Basin

Tropical Storm Hanna moving through northeastern U.S. into the Maritime Provinces (see SHORT RANGE OUTLOOK below)

Category 3 Hurricane Ike north of Haiti, tracking west at about 12 mph (see MEDIUM RANGE OUTLOOK below)

Josephine has dissipated into a vestigial cloud vortex over the eastern Atlantic Ocean

African ITCZ

Four prominent impulses along the discontinuity, stretching from Cape Verde Islands to the Sudan. Development of any of these tropical waves into an organized cyclone is unlikely due to high levels of dry air and dust inhalation, as well as increasing westerly wind profiles over the equatorial Atlantic Basin.

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

Tropical Storm Hanna On A Tear Through The Northeast


Hanna is now rocketing through the Northeast toward Nova Scotia and Newfoundland. A classic example of a split "wind right, heavy rain left" of path tropical cyclone, Hanna should be over the Grand Banks by Sunday night. Up to 6 inches of rain may fall along and 100 miles west of the northern end of the Interstate 95 corridor, while shoreline locations experience winds as high as 55 mph from the system as it merges with a frontal structure.

Chilly Air Takes Over Much Of The Great Plains And Midwest....

The formation of a +PNA, -NAO jet stream configuration over and about North America can lead to some impressive cooling trends in much of Canada and the U.S. Just such an alignment is developing, and the Midwest and interior Northeast will feel the effects of cP intrusions associated with a 500MB mean trough anchored from Manitoba into the Missouri Valley. The eastward and southerly spread of the lower temperatures may take a while to happen, but in the near term people may actually be using heating devices as the longer nights get distinctly chilly in locations such as Minneapolis MN, Denver CO and Buffalo NY.

....While Heat Holds (For Now) Over Dixie And The Southwest

The gradual shift to lower temperatures may not immediately include the southern third of the nation, as a weak (and permeable) subtropical high brings one last dose of summertime weather. Maximum readings in the low or middle 90s (F) are probable from California eastward into the Carolinas, with relative humidity generally low with a surface anticyclone over Texas and the Deep South.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Hurricane Ike: A Double Hit In Florida?



While the spread of the numerical model forecast is still fairly wide, some elements are present which will enable a prediction on the upcoming track and intensity of Hurricane Ike. Ike is already intensifying, and is, as of this writing, moving due westward. The upper level flow ahead of Ike is south-southwest (see the animated satellite imagery), so with such a strong, deep layered storm some recurvature is likely as the hurricane approaches Cuba. The GFDL version sees this factor, hence its solution is favored. Both the GFS and GGEM schemes from 12z took the hurricane into the Gulf of Mexico, then predicted a sharp recurvature into the FL Panhandle on Day 6 (Canadian outlook) or 7 (American version). Since Ike has already lost a southerly component to motion it is possible that interaction with Cuba will be relatively minor, riding along the north shoreline before turning northwestward into Monroe County FL (the Keys and extreme SW corner of the Sunshine State). My leftward variation into S AL would threaten the eastern third of the Gulf energy facilities (a la Ivan 2004) while the easterly deviation would largely affect the Miami and Space Coast metro areas early or middle portion of next week. The solution I am leaning toward may have some eventual analogies to Donna (1960), if Ike does not run into any problems from shear or extensive land interaction from the island of Cuba. Linking with a strong cold front (and there already is a weakness in place from northeastern Mexico into the Southeast in the wake of Hanna and an older frontal structure), Ike may accelerate through the Piedmont into the Northeast by next weekend with concerns similar to Hanna, though on a much larger scale.

I did not accept the scenario offered by the 12z ECMWF, 18z GFS, and some of the tropical forecast models, which either brings the hurricane over the central/western Gulf of Mexico or slides the storm into northern Mexico. The presence of southwest flow aloft and a strong, southeastward advance of a cool intrusion should be enough to turn Ike toward the northeast by September 10 - 11.

Mean 500MB Trough Forms Over The Middle Of North America....

Hurricane Gustav started the process, Tropical Storm Hanna accented it, and I feel that Hurricane Ike is the last cog in the machine, so to speak, in interacting with the impressive series of shortwaves culminating in the eastward advance of a storm complex in the Gulf of Alaska (which the European model mysteriously eliminates, much like the operational GFS scheme constantly underplays the strength of the Ike pressure and circulation pattern). The result, during the medium range, will be a definitive surge of cooler air into the Old South and East Coast following the departure of Ike by September 15 - 16.

....With +PNA Ridge Complex Across The Intermountain Region

A strong ridge over the western states (complimented by a positive height anomaly in the vicinity of Greenland), will allow for a full-latitude trough to set up east of the Rocky Mountains in the wake of Ike. Note that the 12z GFS version shows a cold front AGAIN reaching the Gulf Coast! This frontal structure could create some opportunities for strong to severe thunderstorms over Appalachia and the Atlantic Coastal Plain. But I suspect that its biggest effect will be to make many people realize that summer has ended about a week early, and that it may be useful to turn off the air conditioner while turning on the heat!

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

Prominent Ridges Over Western North America And Greenland Translate To....

The numerical models have been consistent in showing positive height anomalies over western North America and Greenland. This pattern, known as a +PNA (-EPO variant)/-NAO configuration, always favors very chilly temperatures east of the Rocky Mountains. The one notable deviation from this trend has been the persistence of a strong Bermuda High, which, when matched against a vestigial Sonoran heat ridge, teleconnects with a well-developed 500MB trough from central Canada into the lower Mississippi Valley. In essence, the subtropical high over the Atlantic Ocean acts to feed moisture northward into oncoming cold fronts, increasing the threat for repeated heavy rainfall and strong thunderstorms.

Yes, we did see this type of situation in September of 1976. Just in case you were wondering....

Is The "Cape Verde" Portion Of The 2008 Hurricane Season Over?

The answer, unequivocally, is YES. Shearing wind profiles now dominate the equatorial Atlantic Ocean, and computer forecasts through September 22 show the westerlies continuing to impinge on the lower latitudes. The ENSO profile of the Pacific Basin (neutral 3,4 sector, very warm SSTs close to South and Central America) teleconnects well with southwest flow aloft from southern Mexico into the Sargasso Sea, an idea born out by the most recent GFS model forecasts. This is not to say that tropical cyclone threats are completely extinguished from now until the official end of the hurricane season (November 30). Rather it affirms that those systems that DO form will come from "home brew" developments in the Bay of Campeche, western Atlantic Ocean and Sargasso Sea, subtropical formations near the Azores, Bermuda or Gulf Stream, and rogue storms in the Caribbean Sea. I suspect that three or possibly four more named disturbances could develop in those situations.

Prepared by Meteorologist LARRY COSGROVE on
Saturday, September 6, 2008 at 5:55 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

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