EPAC: Tropical Storm Hernan

[cycloneye]

[HURAKAN]

[Cyclenall]

I don't get why the forecast is for strengthening of 6 knots during every 6 hours for the next 24 hours (when shear is still affecting the system) and then doesn't intensify as fast when the shear relaxes. What?

[Chacor]

WTPZ44 KNHC 070831
TCDEP4
TROPICAL STORM HERNAN DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
200 AM PDT THU AUG 07 2008

HERNAN'S CLOUD PATTERN CONTINUES TO GRADUALLY INCREASE IN
ORGANIZATION. THE CENTER IS ESTIMATED TO BE NEAR THE NORTHEASTERN
EDGE OF A NEAR-CENTRAL REGION OF VERY COLD-TOPPED CONVECTION...AND
THIS HAS BEEN CONFIRMED BY MICROWAVE IMAGERY. UPPER-LEVEL OUTFLOW
IS FAIRLY PRONOUNCED OVER THE WESTERN SEMICIRCLE OF THE STORM BUT
IS IMPEDED ON THE EASTERN SIDE. CURRENT INTENSITY IS SET AT 45 KT
BASED ON THE LATEST DVORAK ESTIMATES FROM TAFB AND SAB. EAST-
NORTHEASTERLY VERTICAL SHEAR CONTINUES TO HAVE SOME IMPACT...
HOWEVER THE SHIPS MODEL INDICATES SOME RELAXATION OF THE SHEAR
WITHIN THE NEXT DAY OR TWO. THEREFORE THE ENVIRONMENT SHOULD BE
AMENABLE FOR GRADUAL STRENGTHENING IN THE NEAR FUTURE. THE
OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ONE AND IS
ON THE HIGH SIDE OF THE VARIOUS OBJECTIVE INTENSITY FORECAST
TECHNIQUES. AFTER ABOUT 48 HOURS...HERNAN SHOULD BEGIN TO PASS
OVER COOLER WATERS SO A GRADUAL DECLINE IN STRENGTH IS FORECAST TO
COMMENCE AT THAT TIME.

INITIAL MOTION IS AROUND 295/12. A MID-TROPOSPHERIC RIDGE TO THE
NORTH AND NORTHEAST OF HERNAN SHOULD PERSIST OVER THE NEXT COUPLE
OF DAYS. LATER IN THE PERIOD...HERNAN IS LIKELY TO BE NEARING THE
WESTERN PERIPHERY OF THE RIDGE. HOWEVER BY THAT TIME...THE CYCLONE
WILL BE WEAKENING AND BECOMING SHALLOWER...AND BEING MOVED MORE BY
LOW-LEVEL EASTERLIES. THEREFORE A MORE WESTWARD MOTION IS
INDICATED IN 4 TO 5 DAYS. THE OFFICIAL FORECAST TRACK IS SIMILAR
TO BUT A LITTLE FASTER THAN THE PREVIOUS NHC TRACK. THIS IS FAIRLY
CLOSE TO THE DYNAMICAL MODEL CONSENSUS. THE GFDL MODEL IS AN
OUTLIER AS IT SHOWS A MORE NORTHWESTWARD TRACK THAN THE REST OF THE
MODEL SUITE.

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/0900Z 14.5N 114.0W 45 KT
12HR VT 07/1800Z 15.1N 115.5W 50 KT
24HR VT 08/0600Z 15.8N 117.5W 55 KT
36HR VT 08/1800Z 16.5N 119.4W 65 KT
48HR VT 09/0600Z 17.2N 121.4W 65 KT
72HR VT 10/0600Z 18.5N 125.0W 55 KT
96HR VT 11/0600Z 19.0N 128.0W 40 KT
120HR VT 12/0600Z 19.5N 131.0W 25 KT...REMNANT LOW

$$
FORECASTER PASCH

[KWT]

So they are forecasting a hurricane out of this. The key clearly is the shear relaxing because if it doesn't then they may be too high but if the shear does ease then its got enough time to strengthen into a hurricane.

[Chacor]

EPac has been churning out hurricanes this year...but no majors.

[cycloneye]

WTPZ44 KNHC 071441
TCDEP4
TROPICAL STORM HERNAN DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
800 AM PDT THU AUG 07 2008

THE CLOUD PATTERN HAS CONTINUED TO BECOME BETTER ORGANIZED...BUT
NORTHEASTERLY SHEAR IS KEEPING THE CENTER LOCATED IN THE NORTHERN
PORTION OF VERY STRONG CONVECTION. THE UPPER-LEVEL OUTFLOW IS
WELL-ESTABLISHED EXCEPT TO THE NORTHEAST. THE DVORAK T-NUMBERS HAVE
NOT CHANGED BUT THE CLOUD PATTERN HAS BECOME A LITTLE BETTER
ORGANIZED SINCE THE 12 UTC CLASSIFICATION. SO...THE INITIAL
INTENSITY IS INCREASED TO 50 KNOTS. THE SHEAR IS EXPECTED TO RELAX
A LITTLE ALLOWING HERNAN TO STRENGTHEN SOME AND THE CYCLONE COULD
REACH HURRICANE STRENGTH BEFORE IT MOVES OVER COOLER WATERS IN A
COUPLE OF DAYS. A GRADUAL DECLINE IN STRENGTH IS FORECAST TO
COMMENCE AT THAT TIME. THE OFFICIAL FORECAST IS A LITTLE BIT
HIGHER THAN GUIDANCE AND FOLLOWS THE PREVIOUS FORECAST. IN
FACT...THE GFDL IS THE ONLY MODEL WHICH BRIEFLY BRINGS HERNAN TO
HURRICANE STATUS.

HERNAN IS MOVING TOWARD THE WEST-NORTHWEST OR 295 DEGREES AT 10
KNOTS AROUND THE PERIPHERY OF A SUBTROPICAL RIDGE. SINCE THIS
PATTERN IS FORECAST TO PERSIST...THIS GENERAL MOTION IS EXPECTED TO
CONTINUE FOR THE NEXT 2 TO 3 DAYS. THEREAFTER...AS HERNAN WEAKENS
AND BECOMES A SHALLOW SYSTEM...IT SHOULD TURN MORE TO WEST STEERED
BY THE LOW-LEVEL FLOW. THIS OFFICIAL FORECAST IS CLOSE TO THE
DYNAMICAL MODEL CONSENSUS.


FORECAST POSITIONS AND MAX WINDS

INITIAL 07/1500Z 14.8N 115.1W 50 KT
12HR VT 08/0000Z 15.4N 116.7W 55 KT
24HR VT 08/1200Z 16.0N 118.5W 60 KT
36HR VT 09/0000Z 17.0N 120.0W 65 KT
48HR VT 09/1200Z 17.5N 122.0W 55 KT
72HR VT 10/1200Z 18.5N 125.5W 45 KT
96HR VT 11/1200Z 19.0N 128.5W 35 KT
120HR VT 12/1200Z 19.0N 132.0W 25 KT...REMNANT LOW

$$
FORECASTER AVILA

[HURAKAN]

It looks pretty impressive.

[HURAKAN]

ICU!!!

[HURAKAN]

[Cyclenall]

The 5:00 am and 11:00 am forecast for Hernan was conservative. This could be a hurricane by 8:00 pm tonight. It's organizing and strengthening very quickly. An eye is bound to appear soon...

[KWT]

Yep I think probably 55-60kts is a good estimate right now, given the way the eye has emerged on Microwave.

[HURAKAN]

Useless for Hernán:

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

----- Current Analysis -----
Date : 07 AUG 2008 Time : 163000 UTC
Lat : 14:53:59 N Lon : 115:21:22 W

CI# /Pressure/ Vmax
2.9 /1001.0mb/ 43.0kt

Final T# Adj T# Raw T#
(3hr avg)
2.9 3.1 3.2

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : -68.1C Cloud Region Temp : -60.9C

Scene Type : UNIFORM CDO CLOUD REGION

Positioning Method : FORECAST INTERPOLATION

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

Tno/CI Rules : Constraint Limits : 0.7T/6hr
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

****************************************************

[HURAKAN]

Ragged-eye visible.

[HURAKAN]

EP, 09, 2008080718, , BEST, 0, 148N, 1160W, 55, 994, TS,

07/1800 UTC 14.1N 116.0W T3.5/3.5 HERNAN -- East Pacific Ocean

[KWT]

Yep right in the same place as the Microwave imagery as well.

Hurakan, I personally would have gone with 60kts but the data so far probably only supports 55kts it seems...for now.

[lebron23]

i would of gone with 60 KTS too.

[cycloneye]

WTPZ44 KNHC 072056
TCDEP4
TROPICAL STORM HERNAN DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
200 PM PDT THU AUG 07 2008

THE OVERALL SATELLITE PRESENTATION OF HERNAN HAS INDICATED A GRADUAL
INCREASE IN ORGANIZATION TODAY...BUT MICROWAVE IMAGERY SUGGESTS
THAT THE LOW-LEVEL CIRCULATION CENTER IS STILL A LITTLE NORTH OF
THE MID-LEVEL CENTER...WHICH IN GEOSTATIONARY VISIBLE IMAGERY LOOKS
LIKE AN EYE THAT IS TRYING TO FORM. SUBJECTIVE DVORAK INTENSITY
ESTIMATES AT 18Z WERE A CONSENSUS 55 KT...AND QUIKSCAT EARLIER
TODAY AROUND 1340Z RETRIEVED WINDS OF 50-55 KT. IT IS POSSIBLE THAT
HERNAN HAS BECOME A LITTLE STRONGER THAN THE LATEST DVORAK
ESTIMATES SUGGEST...BUT GIVEN THE SLIGHTLY TILTED STRUCTURE EVIDENT
IN MICROWAVE IMAGERY...THE ADVISORY INTENSITY WILL BE SET TO 55 KT.
NEVERTHELESS...HERNAN APPEARS TO BE ON THE CUSP OF BECOMING A
HURRICANE...AND ALL OF THE OBJECTIVE INTENSITY MODELS FORECAST THAT
TO HAPPEN WITHIN 24 HOURS. THE OFFICIAL FORECAST CALLS FOR HERNAN
TO REACH HURRICANE STATUS A LITTLE SOONER THAN...AND TO PEAK A
LITTLE HIGHER THAN...MOST OF THE GUIDANCE. THE CYCLONE HAS ABOUT
TWO DAYS UNTIL IT REACHES SSTS OF 26 CELSIUS...SO STEADY WEAKENING
IS FORECAST BEYOND THAT TIME...AND AT A LITTLE FASTER RATE THAN
SHOWN BY THE SHIPS AND LGEM.

THE INITIAL MOTION ESTIMATE IS 285/12...BUT IS A LITTLE UNCERTAIN
SINCE IT IS NOT CRYSTAL CLEAR IN MICROWAVE IMAGERY WHERE THE
LOW-LEVEL CENTER IS LOCATED. DESPITE NOT KNOWING THOSE
DETAILS...AND EVEN THOUGH THERE IS A LITTLE SPREAD IN THE TRACK
MODELS...THE OVERALL SYNOPTIC PATTERN IS RELATIVELY STRAIGHTFORWARD
WITH A SUBTROPICAL RIDGE OF MODERATE STRENGTH FORECAST TO REMAIN IN
PLACE OVER THE EASTERN PACIFIC FOR THE NEXT SEVERAL DAYS. HERNAN
SHOULD CONTINUE WEST-NORTHWESTWARD UNTIL REACHING THE COOLER WATERS
IN A FEW DAYS...FOLLOWED BY A WEAKER CYCLONE EVENTUALLY TURNING
WESTWARD IN THE LOW-LEVEL FLOW. THE NEW OFFICIAL TRACK IS A LITTLE
SOUTH OF THE PREVIOUS ONE THROUGH ABOUT 48 HOURS...BUT IS OTHERWISE
NOT CHANGED THAT MUCH...AND IT IS SIMILAR TO THE MODEL CONSENSUS.



FORECAST POSITIONS AND MAX WINDS

INITIAL 07/2100Z 14.8N 116.7W 55 KT
12HR VT 08/0600Z 15.3N 118.1W 65 KT
24HR VT 08/1800Z 15.8N 119.8W 70 KT
36HR VT 09/0600Z 16.5N 121.6W 70 KT
48HR VT 09/1800Z 17.1N 123.4W 70 KT
72HR VT 10/1800Z 18.0N 126.5W 50 KT
96HR VT 11/1800Z 19.0N 130.0W 35 KT
120HR VT 12/1800Z 19.0N 133.5W 25 KT...REMNANT LOW

$$
FORECASTER KNABB

[RL3AO]

EP, 09, 2008080800, , BEST, 0, 149N, 1174W, 55, 994, TS, 34, NEQ, 60, 60, 60, 60, 1008, 225, 20, 0, 0, E, 0, , 0, 0, HERNAN, D,
EP, 09, 2008080800, , BEST, 0, 149N, 1174W, 55, 994, TS, 50, NEQ, 30, 30, 0, 0, 1008, 225, 20, 0, 0, E, 0, , 0, 0, HERNAN, D,

[Chacor]

Will be interesting to see their reasoning for not upping intensity.

WTPZ34 KNHC 080231
TCPEP4
BULLETIN
TROPICAL STORM HERNAN ADVISORY NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
800 PM PDT THU AUG 07 2008

...HERNAN TURNS WESTWARD WITH LITTLE CHANGE IN STRENGTH...

AT 800 PM PDT...0300 UTC...THE CENTER OF TROPICAL STORM HERNAN WAS
LOCATED NEAR LATITUDE 14.9 NORTH...LONGITUDE 117.8 WEST OR ABOUT 755
MILES...1215 KM...SOUTHWEST OF THE SOUTHERN TIP OF BAJA CALIFORNIA.

HERNAN IS MOVING TOWARD THE WEST NEAR 13 MPH...20 KM/HR. A GENERAL
MOTION TOWARD THE WEST-NORTHWEST WITH A DECREASE IN FORWARD SPEED
IS EXPECTED DURING THE NEXT COUPLE OF DAYS.

MAXIMUM SUSTAINED WINDS ARE NEAR 65 MPH...100 KM/HR...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS...
AND HERNAN COULD BECOME A HURRICANE LATER TONIGHT OR FRIDAY.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 994 MB...29.35 INCHES.

REPEATING THE 800 PM PDT POSITION...14.9 N...117.8 W. MOVEMENT
TOWARD...WEST NEAR 13 MPH. MAXIMUM SUSTAINED WINDS...65 MPH.
MINIMUM CENTRAL PRESSURE...994 MB.

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
200 AM PDT.

$$
FORECASTER BEVEN