EPAC : TROPICAL DEPRESSION NORA (17E)

[cycloneye]

TROPICAL DEPRESSION SEVENTEEN-E DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP172009
800 PM PDT TUE SEP 22 2009

SATELLITE IMAGERY INDICATES THAT THE BROAD AREA OF LOW PRESSURE
LOCATED SEVERAL HUNDRED MILES SOUTHWEST OF THE SOUTHERN TIP OF BAJA
CALIFORNIA HAS ACQUIRED SUFFICIENT CONVECTION ORGANIZATION TO BE
DESIGNATED AS A TROPICAL DEPRESSION...THE SEVENTEENTH OF THE
SEASON. THE DEPRESSION IS COMPRISED OF AN ELONGATED AND FAIRLY
SHAPELESS MASS OF CENTRAL CONVECTION...DISPLACED NORTHWEST OF THE
ESTIMATED CENTER DUE TO SOUTHEASTERLY SHEAR. DVORAK T-NUMBERS ARE
T 2.0 FROM BOTH TAFB AND SAB AND SERVE AS THE BASIS FOR SETTING THE
ADVISORY INTENSITY AT 30 KT. WITHIN 24 HOURS... SOUTHWESTERLY SHEAR
IS EXPECTED TO BEGIN INCREASING AND SHOULD BECOME PROHIBITIVELY
STRONG BY 48 HOURS. HOWEVER...PRIOR TO ENCOUNTERING THIS HIGH SHEAR
ENVIRONMENT...THE DEPRESSION HAS SOME OPPORTUNITY TO BECOME A
TROPICAL STORM. WEAKENING IS THEN FORECAST AFTER 36 HOURS...WITH
THE DEPRESSION FORECAST TO BECOME A REMNANT LOW BY 72 HOURS. THE
OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE SHIPS/LGEM GUIDANCE
AND DOES NOT CONSIDER THE GFDL/HWRF INTENSITY FORECASTS WHICH CALL
FOR THE DEPRESSION TO BECOME A HURRICANE. THESE FORECASTS APPEAR TO
BE UNREALISTIC..GIVEN THE STRONG SHEAR FORECAST BY THE GLOBAL
MODELS.

THERE IS MORE UNCERTAINTY THAN NORMAL IN THE INITIAL MOTION...WHICH
IS ESTIMATED AT 320/08. GLOBAL MODELS SHOW A BREAK IN THE
SUBTROPICAL RIDGE BETWEEN 115 WEST AND 120 WEST...WHICH SHOULD
STEER THE DEPRESSION ON A GENERAL NORTHWESTWARD COURSE FOR THE NEXT
24 HOURS. THEREAFTER...THE STRONG SHEAR FORECAST BY THE GLOBAL
MODELS SHOULD CAUSE A DECOUPLING OF THE CYCLONE...WITH THE LOW-
LEVEL CENTER EXPECTED TO TURN TOWARD THE WEST AT A REDUCED
FORWARD SPEED UNTIL DISSIPATION.

FORECAST POSITIONS AND MAX WINDS

INITIAL 23/0300Z 15.7N 115.7W 30 KT
12HR VT 23/1200Z 16.4N 116.5W 35 KT
24HR VT 24/0000Z 17.3N 117.5W 40 KT
36HR VT 24/1200Z 17.6N 118.2W 35 KT
48HR VT 25/0000Z 17.7N 119.0W 30 KT
72HR VT 26/0000Z 17.8N 120.5W 20 KT...REMNANT LOW
96HR VT 27/0000Z...DISSIPATED

$$
FORECASTER KIMBERLAIN

[cycloneye]

WTPZ42 KNHC 230850
TCDEP2
TROPICAL STORM NORA DISCUSSION NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP172009
200 AM PDT WED SEP 23 2009

DURING THE PAST SEVERAL HOURS...THE SYSTEM HAS BEEN TRANSITIONING
FROM A BLOB OF CENTRAL CONVECTION ON SATELLITE IMAGERY TO A SPIRAL
BANDING PATTERN...RESULTING IN A MORE ORGANIZED APPEARANCE. A
QUIKSCAT PASS AT 0218 UTC SUGGESTED THE MAXIMUM WINDS WERE AT LEAST
30 KT AND AN ASCAT PASS AT 0537 UTC GENERALLY SHOWED STRONGER WINDS
THROUGHOUT THE CIRCULATION THAN THE QUIKSCAT...BUT STILL SHOWED A
PEAK WIND SPEED OF ABOUT 30 KT. DVORAK SATELLITE ESTIMATES FROM
TAFB/SAB WERE 35 AND 30 KT...RESPECTIVELY...AT 0600 UTC...WITH AMSU
ESTIMATES OF ABOUT 40-45 KT. AFTER CONSIDERING THE IMPROVED
SATELLITE APPEARANCE AND GENERAL LOW BIAS OF ASCAT...THE INITIAL
INTENSITY WILL BE SET TO 35 KT.

NORA APPEARS TO HAVE ABOUT 24-36 HOURS TO STRENGTHEN BEFORE
SHEAR INCREASES FROM THE SOUTHWEST OR WEST DUE TO A LARGE EASTERN
PACIFIC TROUGH. THE REGIONAL HURRICANE MODELS...HWRF/GFDL...
CONTINUE TO INTENSIFY THE CYCLONE MORE THAN THE STATISTICAL
GUIDANCE...WITH THE HWRF MAKING NORA A HURRICANE BY TOMORROW.
IT IS WORTH POINTING OUT THAT THE SHIPS RAPID INTENSIFICATION INDEX
DOES SHOW A 25 PERCENT CHANCE OF A 30 KT INCREASE DURING THE NEXT
24 HOURS...WHICH IS ABOUT 3 TIMES THE SAMPLE MEAN. THE OFFICIAL
FORECAST IS INCREASED FROM THE PREVIOUS FORECAST BUT REMAINS CLOSER
TO THE STATISTICAL GUIDANCE AT THIS TIME. IN THE LONGER-TERM...
THE HWRF/GFDL PROBABLY SHOW TOO STRONG OF A SYSTEM IN A SHEARED
ENVIRONMENT...A COMMON BIAS OF THOSE MODELS. COOLER WATERS AND
STRONG SHEAR SHOULD PROMOTE WEAKENING OF NORA INTO A REMNANT LOW IN
ABOUT 3 DAYS.

A SERIES OF MICROWAVE PASSES OVERNIGHT HAS HELPED SET THE INITIAL
MOTION TO 310/7...THOUGH THE RECENT ASCAT DATA SUGGEST THE CENTER
COULD BE MOVING A LITTLE MORE TO THE LEFT. A MIDDLE TO UPPER-LEVEL
RIDGE TO THE NORTH IS STEERING THE CYCLONE FOR THE TIME BEING.
THERE IS A FAIR AMOUNT OF MODEL DISAGREEMENT ON WHETHER THE RIDGE
BUILDS WESTWARD...CAUSING A MORE WESTWARD TRACK OF NORA...OR IF THE
MID- TO UPPER-LEVEL TROUGH CURRENTLY OVER THE EASTERN PACIFIC
CAUSES A BREAK IN THE RIDGE...WHICH WOULD ALLOW THE CURRENT
NORTHWESTWARD MOTION TO CONTINUE. THE GFS/GFDL/ECMWF/HWRF
GENERALLY FAVOR A WEST OR WEST-NORTHWEST TRACK FOR THE NEXT FEW
DAYS... WHILE THE NOGAPS AND CANADIAN MODELS SUPPORT A NORTHWESTWARD
MOTION. MY INCLINATION IS TO LEAN TOWARD THE MORE EQUATORWARD
SOLUTION AS THIS SYSTEM SEEMS UNLIKELY TO GET STRONG ENOUGH TO FEEL
THE FULL EFFECTS OF THAT TROUGH. THE OFFICIAL FORECAST IS SHIFTED
TO THE LEFT...BUT IS NOT AS FAR LEFT AS THE MODEL CONSENSUS DUE TO
CONTINUITY CONSIDERATIONS. IT WOULD NOT BE SURPRISING IF THE
FORECAST SHIFTED FARTHER WESTWARD LATER TODAY. IN A FEW DAYS...A
MORE SIGNIFICANT BREAK IN THE RIDGE COULD ALLOW THE SYSTEM TO GAIN
LATITUDE. HOWEVER...IT IS EXPECTED THAT THE CYCLONE WILL BE QUITE
WEAK BY THAT TIME AND UNABLE TO RESPOND TO THAT STEERING FLOW.

FORECAST POSITIONS AND MAX WINDS

INITIAL 23/0900Z 16.1N 116.7W 35 KT
12HR VT 23/1800Z 16.6N 117.5W 45 KT
24HR VT 24/0600Z 17.0N 118.4W 50 KT
36HR VT 24/1800Z 17.2N 119.4W 45 KT
48HR VT 25/0600Z 17.4N 120.6W 35 KT
72HR VT 26/0600Z 17.7N 123.0W 25 KT...REMNANT LOW
96HR VT 27/0600Z 18.0N 125.5W 20 KT...REMNANT LOW
120HR VT 28/0600Z...DISSIPATED

$$
FORECASTER BLAKE

[leanne_uk]

so we now have our Nora, lets see what she can do over the next 24 hours or so

[HURAKAN]

Lookin' good

[HURAKAN]

Loop

[HURAKAN]

Looking great

[HURAKAN]

TROPICAL STORM NORA DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP172009
800 AM PDT WED SEP 23 2009

NORA HAS BECOME A LITTLE BETTER ORGANIZED THIS MORNING...AS A
CENTRAL CONVECTIVE FEATURE HAS FORMED WITH AN OUTER BAND IN THE
WESTERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM
TAFB AND 35 KT FROM SAB...AND BASED ON THIS THE INITIAL INTENSITY
IS INCREASED TO 40 KT. THE CIRRUS OUTFLOW IS CURRENTLY FAIR TO
GOOD IN ALL DIRECTIONS.

THE INITIAL MOTION IS 300/8...A LITTLE TO THE LEFT AND SLIGHTLY
FASTER THAN PREVIOUSLY. NORA IS ON THE SOUTH SIDE OF A LOW-LEVEL
RIDGE...AND ALSO SOUTH OF A WEAKNESS IN THE MID-LEVEL RIDGE. THE
LARGE-SCALE MODELS FORECAST THE LOW-LEVEL RIDGE TO REMAIN IN PLACE
FOR THE NEXT SEVERAL DAYS WHILE A MID/UPPER-LEVEL LOW FORMS TO THE
NORTHWEST OF NORA. THIS EVOLUTION SHOULD STEER NORA GENERALLY
WEST-NORTHWESTWARD OR WESTWARD FOR THE NEXT 24-36 HR. THE MOTION
BEYOND THAT TIME DEPENDS ON HOW STRONG NORA GETS. A STRONGER AND
VERTICALLY DEEPER SYSTEM SHOULD TURN MORE TOWARD THE NORTHWEST AS
FORECAST BY THE GFDL...HWRF...AND CANADIAN MODELS. A WEAKER AND
SHALLOWER NORA SHOULD MOVE MORE WESTWARD AS FORECAST BY THE
BAMS...GFS...AND ECMWF. THE TRACK FORECAST WILL LEAN TOWARD THE
LATTER SCENARIO...WITH A SLOW AND GENERALLY WESTWARD MOTION AFTER
36 HR.

NORA IS CURRENTLY IN AN ENVIRONMENT OF LIGHT SOUTHERLY VERTICAL WIND
SHEAR. THE LARGE-SCALE MODELS SUGGEST THAT THE CYCLONE WILL REMAIN
IN A FAVORABLE ENVIRONMENT FOR ABOUT 24 HR MORE...FOLLOWED BY A
SIGNIFICANT INCREASE IN THE SHEAR AS NORA REACHES COOLER SEA
SURFACE TEMPERATURES. THIS SUGGESTS THAT NORA SHOULD STRENGTHEN
FOR A DAY OR SO...FOLLOWED BY A STEADY WEAKENING. THE NEW
INTENSITY FORECAST FOLLOWS THE SHIPS AND LGEM GUIDANCE...CALLING
FOR A PEAK INTENSITY OF 55 KT IN 24 HR AND WEAKENING TO A REMNANT
LOW BY 72 HR. THE SHIPS RAPID INTENSIFICATION INDEX SHOWS A
25 PERCENT CHANCE OF A 30 KT INCREASE IN STRENGTH DURING THE NEXT
24 HR...SO IT CANNOT BE RULED OUT THAT NORA COULD BECOME A HURRICANE
BEFORE ENCOUNTERING THE STRONGER SHEAR. THE GFDL AND HWRF SUPPORT
THIS POSSIBILITY BY FORECASTING NORA TO BECOME A HURRICANE.
HOWEVER...THIS OCCURS IN BOTH MODELS ONLY AFTER THE STRONGER SHEAR
DEVELOPS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 23/1500Z 16.5N 117.5W 40 KT
12HR VT 24/0000Z 16.9N 118.4W 50 KT
24HR VT 24/1200Z 17.1N 119.4W 55 KT
36HR VT 25/0000Z 17.2N 120.4W 50 KT
48HR VT 25/1200Z 17.3N 121.4W 40 KT
72HR VT 26/1200Z 17.5N 123.5W 25 KT...REMNANT LOW
96HR VT 27/1200Z 18.0N 126.0W 20 KT...REMNANT LOW
120HR VT 28/1200Z...DISSIPATED

$$
FORECASTER BEVEN

[HURAKAN]

Very nice system

[CrazyC83]

Rapid deepening underway? It mentions Hurricane Nora being a distinct possibility, when yesterday the thought seemed laughable.

[HURAKAN]

Latest

[CrazyC83]

Seems to be an eyewall forming.

[Derek Ortt]

there's no eyewall on the microwave

Just a gradually intensifying TS

[HURAKAN]

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 23 SEP 2009 Time : 163000 UTC
Lat : 16:35:14 N Lon : 117:39:00 W


CI# /Pressure/ Vmax
3.3 / 996.4mb/ 51.0kt


Final T# Adj T# Raw T#
(3hr avg)
3.3 3.5 3.5

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : -63.6C Cloud Region Temp : -48.4C

Scene Type : CURVED BAND with 0.38 ARC in WHITE

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : EAST PACIFIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

[HurricaneRobert]

This will probably be Hurricane Nora as the models have been predicting. It looks so much better this afternoon.

[HURAKAN]

23/1800 UTC 16.7N 118.3W T3.0/3.0 NORA -- East Pacific

Dvorak says 50 mph

[cycloneye]

18 UTC Best track increase winds to 45kts.

EP, 17, 2009092318, , BEST, 0, 167N, 1183W, 45, 1002, TS

ftp://ftp.tpc.ncep.noaa.gov/atcf/tcweb/ ... 009.invest

[Kingarabian]

I think 45 kts is to conservative.

[cycloneye]

TROPICAL STORM NORA DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP172009
200 PM PDT WED SEP 23 2009

THE ORGANIZATION OF THE CLOUD PATTERN IS DEFINITELY IN AN UPWARD
TREND. THE PATTERN RESEMBLES A NUMBER SIX WITH A WELL DEFINED
CYCLONICALLY-CURVED CONVECTIVE BAND WHICH WRAPS AROUND A SMALL
CENTRAL DENSE OVERCAST. THERE ARE NO SIGNS OF SHEAR GIVEN
THAT THE OUTFLOW IS FAIR IN ALL DIRECTIONS. T-NUMBERS FROM BOTH TAFB
AND SAB ARE 3.0 ON THE DVORAK SCALE...AND BASED ON THESE NUMBERS...
THE INITIAL INTENSITY IS SET AT 45 KNOTS. NORA HAS A DAY OR TWO TO
STRENGTHEN BEFORE THE SHEAR INCREASES AS INDICATED BY MOST OF THE
GLOBAL MODELS. THE OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS
ONE AND FOLLOWS THE SHIPS MODEL. THE GFDL/HWRF MODEL PAIR MAKES
NORA A HURRICANE IN A DAY OR SO AND ALTHOUGH THIS SOLUTION DOES NOT
SEEM LIKELY AT THIS TIME...IT IS NOT OUT OF THE QUESTION.

BEST ESTIMATE OF THE INITIAL MOTION IS 290 DEGREES AT 6 KNOTS.
GLOBAL MODELS INDICATE THAT THE SUBTROPICAL RIDE NORTH OF NORA WILL
EXPAND WESTWARD. THIS PATTERN SHOULD FORCE NORA TO TURN MORE TO THE
WEST DURING THE NEXT TWO TO THREE DAYS BEFORE NORA BECOMES A
REMNANT LOW. IN FACT...THE MODEL CONSENSUS SHOWS A DEFINITELY
WESTWARD TRACK DURING THE NEXT THREE DAYS AND SO DOES THE OFFICIAL
FORECAST. THE GFDL/HWRF PAIR MOVE NORA ON A MORE NORTHERLY TRACK
BUT THIS SOLUTION DOES NOT APPEAR TO BE REALISTIC AT THIS TIME WITH
THE EXPECTED STEERING PATTERN.

FORECAST POSITIONS AND MAX WINDS

INITIAL 23/2100Z 16.8N 118.6W 45 KT
12HR VT 24/0600Z 17.2N 119.6W 55 KT
24HR VT 24/1800Z 17.3N 120.5W 55 KT
36HR VT 25/0600Z 17.3N 121.5W 50 KT
48HR VT 25/1800Z 17.3N 122.5W 40 KT
72HR VT 26/1800Z 17.5N 125.5W 30 KT
96HR VT 27/1800Z 19.0N 128.0W 20 KT...REMNANT LOW
120HR VT 28/1800Z 20.5N 130.0W 20 KT...REMNANT LOW

$$
FORECASTER AVILA

[Kingarabian]

[leanne_uk]

Nora is developing quickly into a stunning storm. The latest pictures above are fantastic