Tropical Storm Karen

Update: October 5, 10:03 p.m. The NHC considers Karen barely a tropical storm as of this afternoon’s forecast discussion.

Surge probabilities per the NHC have really dropped for most locations, as Karen nears landfall, with low probability of surge greater than 2 feet only in Houma, Louisiana; Gulfport, Mississippi, and environs; and Mobile, Alabma.

Storm Surge October 5

Right now, the GFS doesn’t show Karen’s remnants harassing the East Coast, as it did on earlier runs, fortunately.

Jeff Masters sums up the outlook for Karen today:

Forecast for Karen

The computer models have come into good agreement on the track of Karen, with the storm expected to make landfall in Southeast Louisiana and pass near or to the south of New Orleans early Sunday morning. With wind shear showing no signs of letting up, any strengthening of Karen on Saturday will be slow, and it is more likely that the storm will weaken to a tropical depression with 35 mph winds before landfall. NHC’s 11 am EDT Saturday wind probability forecast shows the highest odds of tropical storm-force winds to be at the tip of the Mississippi River at Buras, Louisiana: 47%. New Orleans has a 38% chance, and the rest of the coast from Mississippi to Pensacola, Florida has odds ranging from 20% – 30%. Karen should cause mostly minor damage at landfall, with flooding rains, storm surge, and a few weak tornadoes of concern.

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All that brown and black is dry air that, along with fairly strong wind shear, is keeping Tropical Storm Karen from developing quickly.  Click to enlarge. (GOES water vapor imagery)

All that brown and black is dry air that, along with fairly strong wind shear, is keeping Tropical Storm Karen from developing quickly. The purple, orange and other bright colors show Karen is ready to really start kicking, if given a chance. (GOES water vapor imagery)

Update, October 4, 2013, at 11:01 a.m. Eastern:

We’re very lucky in the Gulf with this one. If there weren’t strong limiting factor in place – nearby dry air that Karen is drawing in, thus weakening the storm, and fairly strong wind shear – this baby could easily turn into something major very quickly.

The powers that be aren’t messing around, though. NASA sent in a jet overnight to get better data of the environment around Karen, as you will see in the NHC’s 11 a.m. forecast discussion this morning, which sums up the situation – and the question about Karen’s future intensity and course – very well (emphasis and comment added):

WTNT42 KNHC 041432
TCDAT2

TROPICAL STORM KAREN DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122013
1000 AM CDT FRI OCT 04 2013

AFTER BEING DISPLACED WELL EAST OF THE LOW-LEVEL CENTER OF KAREN…DEEP CONVECTION HAS RECENTLY DEVELOPED A LITTLE CLOSER TO THE CENTER OVER THE PAST HOUR OR TWO…BUT THE CYCLONE IS STILL BEING AFFECTED BY 20-25 KT OF WESTERLY SHEAR AND DRY AIR BEING ADVECTED INTO THE CYCLONE. THE LAST CENTRAL PRESSURE REPORTED BY THE AIRCRAFT WAS 1003 MB…AND BASED ON THE LATEST ROUND OF AIRCRAFT DATA THE INTENSITY HAS BEEN REDUCED TO 45 KT. THE ENVIRONMENT DOES NOT LOOK FAVORABLE FOR SIGNIFICANT INTENSIFICATION…WITH MODERATE SHEAR EXPECTED TO CONTINUE FOR THE NEXT DAY OR TWO. HOWEVER…IF THE SHEAR DOES LESSEN…EVEN FOR A SHORT PERIOD OF TIME…DEEP CONVECTION COULD RE-DEVELOP CLOSER TO THE CENTER AND ALLOW FOR SOME INTENSIFICATION. IN ADDITION…BY 48 HOURS UPPER-LEVEL DIVERGENCE AHEAD OF AN APPROACHING MID/UPPER-LEVEL TROUGH COULD ALLOW FOR SOME STRENGTHENING. THE NEW NHC INTENSITY FORECAST HAS BEEN ADJUSTED DOWNWARD AND SHOWS LITTLE CHANGE IN THE NEXT 24 HOURS AND A STRENGTHENING TO 55 KT BY 48 HOURS. {Note – This is still only tropical storm strength … Barb)

THE INITIAL MOTION HAS BEEN WOBBLING BETWEEN 325 AND 330 DEGREES AT ABOUT 9 OR 10 KT OVER THE PAST FEW HOURS. THE FUTURE TRACK WILL BE QUITE SENSITIVE TO THE STRUCTURE OF KAREN OVER THE NEXT COUPLE OF DAYS. IN THE SHORT TERM A WEAKER SHALLOWER SYSTEM WILL BE STEERED MORE TOWARD THE LEFT BY THE LOW-LEVEL FLOW…WHILE A DEEPER MORE VERTICALLY COHERENT CYCLONE WOULD TURN NORTHWARD MORE QUICKLY DUE TO A MID-LEVEL RIDGE TO THE EAST. GIVEN THE CURRENT APPEARANCE OF KAREN AND THE CONTINUED SHEAR…THE NHC TRACK HAS BEEN ADJUSTED A
LITTLE TO THE LEFT DURING THE FIRST 24 HOURS TOWARD THE UKMET AND ECMWF MODELS…WHICH SHOW A WEAKER SYSTEM. ALL OF THE GUIDANCE SHOWS A NORTHEASTWARD TURN IN 36 TO 48 HOURS…BUT WITH LARGE DIFFERENCES IN THE LATITUDE AT WHICH THE TURN OCCURS AND SIGNIFICANT SPREAD IN WHERE THE CENTER CROSSES THE COAST. AT 36 HOURS AND BEYOND THE NHC TRACK IS CLOSE TO THE ECMWF AND THE MULTI-MODEL CONSENSUS…AND CLOSE TO THE PREVIOUS OFFICIAL FORECAST. GIVEN THE LARGE SPREAD AND THE DEPENDENCE OF THE TRACK ON THE STRUCTURE AND INTENSITY OF KAREN…CONFIDENCE IN THE DETAILS OF THE TRACK FORECAST…AND THEREFORE THE DISTRIBUTION OF IMPACTS ALONG THE COAST…IS LOW.

THE NOAA GULFSTREAM-IV JET SAMPLED THE ENVIRONMENT NEAR KAREN AND OVER THE NORTHERN GULF OF MEXICO OVERNIGHT. THESE DATA WILL BE INCORPORATED INTO THE 12Z MODEL CYCLE…AND HOPEFULLY IMPROVE THE ANALYSIS OF THE ENVIRONMENT NEAR AND AHEAD OF THE STORM.

GIVEN THE WESTWARD SHIFT IN THE NHC TRACK…THE TROPICAL STORM WARNING HAS BEEN EXTENDED WESTWARD TO MORGAN CITY LOUISIANA. GIVEN THE WEAKENING TREND AND THE REDUCTION IN THE INTENSITY FORECAST…IT HAS BECOME A LITTLE LESS LIKELY THAT KAREN WILL REACH HURRICANE STRENGTH. IF THESE TRENDS CONTINUE…THE HURRICANE WATCH COULD BE CHANGED TO A TROPICAL STORM WATCH OR WARNING LATER TODAY.

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Update, October 3, 2013, at 11:05 a.m. Eastern: The Hurricane Hunter aircraft this morning found a closed circulation, and so with the 8 a.m. NHC bulletin, 97L became Tropical Storm Karen, completely skipping the tropical depression stage.

Actually, I thought it looked like a tropical storm this morning just before 6 a.m. Scientists – always insisting on data!

The current NHC bulletin has just come out. They say the storm has a sheared appearance and that shear will increase, but Karen nonetheless may be close to hurricane strength at landfall.

Where will landfall be? Here is the current five-day NHC forecast cone (note the transition to hurricane status out in the mid-Gulf – that’s impressive for a storm with this much shear over it already):
 

National Hurricane Center

National Hurricane Center


 
This is a good time to mention the NHC wind probabilities chart – not the graphics that they put up on their front page, but the actual sciency-looking printed chart.

I’ve tested it against actual outcomes in some seasons, and it is quite informative, though you do have to think about it more than you would with a graphic. That’s rewarding: It gives you more detailed information about specific places than the forecast cone can deliver.

That’s why the NHC puts out both (and much, much more, too).

science

All you have to do is locate a city on there that is close to your location (or whatever location you’re interested in), say, Mobile, Alabama. Here’s the chart for that.

II. WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS

CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST
…34 KT (39 MPH… 63 KM/H)…
…50 KT (58 MPH… 93 KM/H)…
…64 KT (74 MPH…119 KM/H)…
FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS

PROBABILITIES FOR LOCATIONS ARE GIVEN AS IP(CP) WHERE
IP IS THE PROBABILITY OF THE EVENT BEGINNING DURING
AN INDIVIDUAL TIME PERIOD (INDIVIDUAL PROBABILITY)
(CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN
12Z THU AND THE FORECAST HOUR (CUMULATIVE PROBABILITY)

PROBABILITIES ARE GIVEN IN PERCENT
X INDICATES PROBABILITIES LESS THAN 1 PERCENT
PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN
THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT.
PROBABILITIES FOR 64 KT ARE SHOWN WHEN THE 5-DAY CUMULATIVE
PROBABILITY IS AT LEAST 1 PERCENT.

– – – – WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS – – – –

FROM FROM FROM FROM FROM FROM FROM
TIME 12Z THU 00Z FRI 12Z FRI 00Z SAT 12Z SAT 12Z SUN 12Z MON
PERIODS TO TO TO TO TO TO TO
00Z FRI 12Z FRI 00Z SAT 12Z SAT 12Z SUN 12Z MON 12Z TUE

FORECAST HOUR (12) (24) (36) (48) (72) (96) (120)
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

MOBILE AL 34 X 1( 1) 7( 8) 13(21) 27(48) 1(49) X(49)
MOBILE AL 50 X X( X) X( X) 3( 3) 10(13) 1(14) X(14)
MOBILE AL 64 X X( X) X( X) X( X) 2( 2) 1( 3) X( 3)

It’s not hard to translate that science-speak into English. Right now, they think Mobile’s chances of starting to experience low-end tropical storm winds (34 knots/39 mph/63 kph) – individual probability or IP – are highest in 72 hours (27%). The chances of such winds being ongoing – cumulative probability or CP – is pretty high from 72 hours(48%), through 96 hours (49%), to the end of the period (120 hours – 49%).

For strong tropical storm winds (50 knots/58 mph/93 kph), Mobile’s chances are still highest at 72 hours for it starting and then continuing from 72-120 hours, but they’re really not very high.

For barely Category 1 hurricane winds (64 knots/74 mph/119 kph), Mobile’s IP and CP changes, while highest during the same time frame, are pretty low.

See how it works? If you’re in Mobile, you’re most likely to experience low-end tropical storm winds from TS Karen, if you experience anything at all (the forecast cone shifts with time and as better data comes in).

I find it easiest to use this chart by printing it out and highlighting the various numbers. Just with a quick glance today, I don’t think Mobile is showing the highest probabilities today, but I’ll leave it to you to figure out which of all those listed locations is the one looks most likely now to eventually take a low-end or strong tropical storm strength hit, or a hurricane strength hit.

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Current Funktop infrared imagery of 97L highlights the areas of greatest precipitation.  (GOES)

Current Funktop infrared imagery of 97L highlights the areas of greatest precipitation. Luckily for Mexico (already hard hit by previous storms) and western Cuba, the heaviest rain is falling over over the Yucatan Channel. (GOES)

Update 5:43 a.m. Eastern, October 3rd: Jerry is now a tropical depression out there in the Atlantic, but apparently the NHC is ready to upgrade 97L directly to Tropical Storm Karen later today, per their 2 a.m. tropical outlook (emphasis added):

THE LOW PRESSURE AREA OVER THE NORTHWESTERN CARIBBEAN SEA IS NOW
CENTERED NEAR THE NORTHEASTERN TIP OF THE YUCATAN PENINSULA OF
MEXICO. WHILE THE CIRCULATION IS NOT YET WELL DEFINED…GALE-FORCE
WINDS ARE OCCURRING EAST OF THE CENTER OVER THE YUCATAN CHANNEL.
THIS SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL STORM AT ANY
TIME TODAY
AS IT MOVES NORTH-NORTHWESTWARD INTO THE SOUTHERN GULF
OF MEXICO. THIS SYSTEM HAS A HIGH CHANCE…80 PERCENT…OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
AFTER
THAT…LESS CONDUCIVE UPPER-LEVEL WINDS COULD LIMIT DEVELOPMENT AS
THE SYSTEM APPROACHES THE NORTHERN GULF OF MEXICO THIS WEEKEND.
THIS SYSTEM HAS A HIGH CHANCE…80 PERCENT…OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 5 DAYS. INTERESTS IN THE NORTHEASTERN
YUCATAN PENINSULA…WESTERN CUBA…AND THE NORTHERN GULF COAST
SHOULD MONITOR THE PROGRESS OF THIS SYSTEM. LOCALLY HEAVY RAINS
COULD AFFECT PORTIONS OF CUBA AND THE YUCATAN PENINSULA DURING THE
NEXT DAY OR TWO. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS
SCHEDULED TO INVESTIGATE THE LOW LATER THIS MORNING.

If the current GFS graphic verifies, Georgia and the Carolinas – and possibly as far north as Cape Cod – may also be looking at rain and stormy conditions, but not tropical weather, during the first part of next week from this.

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Pop quiz:  Which one's the cat and which one the mouse?  (Guilhem Vellut)

Pop quiz: Which one’s the cat and which one the mouse? (Guilhem Vellut)

Update, October 2, 2013, 12:09 p.m. Eastern: Tropical Storm Jerry is still out there in the Atlantic, just meandering around – looking for Tom, I suppose.

Closer to land, the expected path and development for 97L still remains pretty much the same as yesterday’s expectations, per this morning’s tropical weather outlook from the NHC. They are sending a Hurricane Hunter craft out this afternoon to investigate it.

As this amateur reads the current GFS run, the system will eventually end up a little more east than it showed yesterday, sitting off the coasts of Mississippi and Alabama, and perhaps even affecting northwestern Florida, too, in 72 hours, and then going inland – could be a nice rain event for the US Southeast.

However, that’s just one model, and I’m not a trained meteorologist. Jeff Masters is and here is his take on things as of this morning along with a nice graphic about possible wind speeds at landfall, including this excerpt:

97L is looking pretty feisty this morning.  (GOES)

97L is looking pretty feisty this morning. Things are stormy this morning on the Caymans. (GOES)

Forecast for 97L: development into at least a tropical depression likely
Wind shear is expected to remain low on Wednesday, then steadily increase to the moderate range on Thursday, then to the high range on Friday, according to the latest SHIPS model forecast. On Wednesday night, 97L will cross the northeastern tip of Mexico’s Yucatan Peninsula, bringing 3 – 6″ of rain to the peninsula and to Western Cuba. Passage over the Yucatan will act to disrupt the storm. The atmosphere will grow drier as 97L moves northwards over the Gulf of Mexico on Thursday and Friday, and the drier air combined with increasing wind shear will retard development, making rapid intensification unlikely. A trough of low pressure and an associated cold front will be moving through Louisiana on Saturday, and the associated upper-level westerly winds will be able to turn 97L more to the northeast as it approaches the coast on Friday. The GFS model develops 97L into a tropical storm, and predicts landfall will occur along the Florida Panhandle. The European model, which does not develop 97L into a tropical storm, is farther west, taking the storm over Eastern Louisiana. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave 97L 2-day odds of development of 40%, and 5-day odds of 50%. I give a 30% chance 97L will be Tropical Storm Karen with top winds of 40 – 60 mph at landfall between Louisiana and the Florida Panhandle on Saturday, a 5% chance it will be stronger, and a 65% chance it will be a tropical depression or mere tropical disturbance. Heavy rains of 3 – 6″ can be expected falling the coast from Louisiana to the Florida Panhandle on Saturday, even if 97L does not develop into a tropical depression.

From a safe distance, though, these systems can be very beautiful. Here is a view of dawn this morning as seen through 97L’s clouds:

Diane Campbell

Diane Campbell, a Storm Carib Belize correspondent.

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Image source:  NASA by way of Wunderground.

Image source: NASA by way of Wunderground.

Wind shear is taking its toll on Tropical Storm Jerry out in the Atlantic, but it has dropped over the Caribbean, and 97L is perking up like a brown lawn after a rainstorm.

Jeff Masters says that a Hurricane Hunter aircraft may be sent in this afternoon or tomorrow, if the area gets more organized. He also gives it a 40% chance of reaching tropical storm strength and becoming Karen.

The National Hurricane Center today gives it a 30% chance of developing into a tropical cyclone in the next two days. Over five days, they give it a 50% chance.

I wanted to mention this now because the models are coming into closer agreement, that when this does reach the Gulf of Mexico, it will head for Louisiana rather than Florida. It’s still far in the future, and things could change.

The good news is that, wherever it ends up, the computer models currently don’t show it strengthening to more than a tropical depression, per Dr. Masters.

Of course, today it’s raining over parts of Cuba, Jamaica and the Cayman Islands. A flooding river has affected 60 homes in Haiti and some of them have collapsed, per the Storm Carib Haiti correspondent.



Categories: Weather

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