Severe Tropical Cyclone Oli

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WTPS21 PGTW 311500

MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//

SUBJ/TROPICAL CYCLONE FORMATION ALERT//

RMKS/

1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN

245 NM EITHER SIDE OF A LINE FROM 10.3S 171.1W TO 12.2S 163.1W

WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY

ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.

WINDS IN THE AREA ARE ESTIMATED TO BE 25 TO 30 KNOTS. METSAT IM-

AGERY AT 311200Z INDICATES THAT A CIRCULATION CENTER IS LOCATED

NEAR 10.7S 170.3W. THE SYSTEM IS MOVING EASTWARD AT 12 KNOTS.

2. REMARKS:

THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 11.0S 173.6W, IS NOW

LOCATED NEAR 10.7S 170.3W, APPROXIMATELY 220 NM NORTH OF PAGO PAGO.

AS OF 1258Z SEA LEVEL PRESSURE HAS DROPPED TO 999.8 MB AT PAGO PAGO,

REPRESENTING A 1.7 MB DEPARTURE FROM 24 HOURS AGO. DVORAK INTENSITY

ESTIMATES FROM PGTW AND PHFO HAVE INCREASED TO A 2.0 DATA-T OR 30

KNOTS. MICROWAVE IMAGERY OVER THE PAST 06 TO 12 HOURS HAS CONTINUED

TO INDICATE A STRENGTHENING LOW LEVEL CIRCULATION CENTER (LLCC) IN

CLOSE PROXIMITY TO DEEPENING AND EXPANDING CENTRAL CONVECTION.

BANDING FEATURES, PARTICULARLY IN THE LOWER LEVELS, HAVE ALSO

CONTINUED TO MATURE AS THEY FEED INTO THE LLCC. THE UPPER LEVEL

RIDGE AXIS HAS ALSO MOVED CLOSER TO THE SYSTEM, RELAXING VERTICAL

WIND SHEAR. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 25 TO

30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 999 MB.

THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE

WITHIN THE NEXT 24 HOURS IS GOOD.

3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY

011500Z.//

NNNN

[Somerset Squall]

Invest 90P has continued to consolidate overnight, and has now been declared a tropical cyclone by JTWC, 300 miles northeast of Pago Pago, which was near where Nisha formed. Some solid, and intense convection has persisted over a well defined LLC, and 12P seems to be in a good environment for some faster than climatological strengthening. Intensity is at 45kts at present, and JTWC seem quite keen to bring the system to 95kt intensity quite rapidly as low shear, warm sea temps (28-30C) and good outflow support intensification. 12P is currently moving eastwards along the southern periphery of an equatorial ridge. The steering influence is strong, and as a result, 12P is moving at a faster than average 16kts. Eventually, the ridge will weaken but also re-orientate to the northeast and east of 12P, forcing the cyclone southeastward or even eventually southward. At around 72hrs, this will take 12P into much higher shear and rapidly declining ocean heat content, which will induce extratropical transition. No large landmass is threatened by 12P, but the islands of Bora Bora, Tahiti and to some extent Rarotonga (if 12P moves southward earlier than anticipated) need to closely watch 12P as the cyclone is expected to pass through these areas in the next few days.

[Somerset Squall]

Fiji Met has upgraded the system to TC Oli. Pressure is falling fairly swiftly, and is currently 995mb.

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[Somerset Squall]

Oli has remained at a steady intensity of 50kts overall over the last 24hrs, with occasional fluctuations to 45kts. Bursting convection has rotated around Oli's LLC, but a central dense overcast feature has not formed. Forecasts are less aggressive with the intensification of Oli over the next couple days, primarily on the lack of rapid intensification observed despite a good environment. However, strengthening should occur over the next 72hrs as shear remains low within this time frame, and waters warm. Eventually, Oli will reach cooler waters and higher shear which should induce extratropical transition as Oli turns south.

[Somerset Squall]

Oli has resumed strengthening, and is now a 65kt, cat 1 on the SS scale. A rugged eye is developing within a strong central dense overcast feature. In addition, banding has improved vastly since last night. Conditions remain favourable for the next 48hrs, with sea temperatures remaining warm, shear low and outflow good. This should allow Oli to intensify further, and I think the cyclone could approach 100kts in intensity before waters cool and shear increases beyond 48hrs. Bora Bora and Tahiti need to make final preperations as Oli is nearing and will move close by or directly over the two islands as a strengthening tropical cyclone.

Oli is moving east-southeastwards along the southern periphery of an equatorial ridge. This motion should shift to southeasterly as a new ridge builds in towards the east or northeast. This ridge will be responsible for taking Oli over the cooler waters.

[Somerset Squall]

Oli has been upgraded to a severe tropical cyclone by Fiji Met. Intensity continues to increase, and is now at 70kts. The eye has become increasingly well defined though a second eyewall has appeared which might be Oli beginning an eye wall replacement cycle. I'm not certain about this, but if an EWRC has begun then there will be a holt in intensification. All the ingredients are still there for a 100kt system however, IMO.

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Like you say mate looking good again

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strongest system in the south Pacific since January 2008.

[Somerset Squall]

Yes, Oli has strengthened rapidly this afternoon and is now a 115kt, cat 4. Pressure has fallen to 925mb, and Oli is exhibiting a well defined eye embedded in the central dense overcast feature. Oli has another 24hrs in which to strengthen further, just how much stronger he can get is uncertain. Thereafter, stronger shear and colder waters will induce weakening.

[Cookie]

now the strongest since Percy in 2005 very impressive system indeed

[Somerset Squall]

Oli peaked at 115kts in the end, and has since accelerated southeastwards into cooler waters and higher shear. This has caused Oli to transform into an extratropical storm. Oli will continue eastwards as a baroclinic low.