central pacific Hurricane Ana

[Somerset Squall]

A disturbance that moved into the Central Pacific from the East Pacific last night has become the second tropical depression to form in the Central Pacific in 2014. 02C has winds of 30kts and consists of a tight LLC with slightly displaced convection and a prominant banding feature wrapping in from the north. 02C is forecast to strengthen into a hurricane by CPHC. Waters are definitely warm enough, but shear values look high to the depression's northwest, which is where 02C is headed.

 

02C is located just west of 140W and a little north of 10N in the image, which shows the strong shear northwest of the depression:

 

 

Unless this eases, I find it hard to believe 02C will become a hurricane. CPHC obviously expect that shear to ease, and they are of course the experts!

 

Track wise, 02C is expected to head westwards on the south side of a ridge to the north.  An approaching trough is expected to shunt the ridge eastwards in the coming days, creating a weakness and sending 02C to the northwest. Now this is quite significant. If CPHC's forecast verifies, 02C will impact Hawaii as a hurricane. It would be the second strike of the year (the first was Iselle). A lot could change of course, but it is interesting to note.

 

 

 

 

 

 

 

 

[Somerset Squall]

02C has become Tropical Storm Ana, with winds of 40kts. Convection has increased greatly overnight, morphing into a central dense overcast. This structure, with the currently low shear over the system, suggests that Ana could strengthen fairly quickly over the next day or so. Higher shear values are still present near Hawaii, and unless this eases or shifts away then Ana will weaken long term. The current track forecast still puts Hawaii in the firing line of Ana.

[Somerset Squall]

Ana has continued to strengthen. Winds are up to 55kts in the latest CPHC advisory. CPHC have acknowledged the high shear between Ana and Hawaii, but this is expected to ease as the upper level low responsible for it moves away. This is not good news for Hawaii, as the track forecast hasn't shifted much, and still points at Ana getting very near Hawaii in 4 days time.

 

Ana has some very cold cloud tops over the LLCC, a sure sign of an intensifying storm:

 

 

 

[Somerset Squall]

Moderate shear has slowed the intensification of Ana today. Winds have increased slightly, to 60kts. The LLCC is estimated to be near the northern edge of the central dense overcast. However, the convection remains very deep, and the shear is expected to ease once again tonight, so Ana could become a hurricane by morning. The track forecast still has Hawaii in the firing line for a hurricane strike from Ana.

[Somerset Squall]

It seems I was right to initially be suspicious of the high shear to the northwest of Ana. Ana has run into this shear, and the area of shear has not moved away. As a consequence, Ana has weakened to 50kts. The central dense overcast that Ana has maintained for a day or so has broken up, and the majority of the remaining convection is displaced south of the LLCC. shear is still expected to ease, but I think there is an equal chance that it won't. Intensity forecasts from CPHC have gradually trended downwards, and they now only expect a peak of 65kts (still a minimal hurricane) as opposed to the earlier 80kt peak forecast. Unless Ana shows signs of recovery soon, I think the chances for Ana to become a hurricane will be rather slim. Track forecast still points to Ana impacting Hawaii, though which of the islands will be impacted the most is still open to question.

[Somerset Squall]

Ana looks much better today as the shear has, at long last, eased. Winds are up to 55kts. Convection has made a significant comeback, and there are hints of an eye trying to form. Track has shifted further west than originally anticipated, meaning Ana may pass southwest of the Big Island of Hawaii (it will still bring adverse weather here) but will probably impact the other islands.

Edited October 17, 2014 by Somerset Squall

[Somerset Squall]

Ana has become a 65kt hurricane. Ana could strengthen a little more over the next 12hrs before shear rises near the Hawaiian Islands, which should produce some weakening. As Ana clears the Hawaiian Islands, some re intensification could occur as shear is expected to ease and waters are anonmolously warm to the west of Hawaii.

[Somerset Squall]

Ana has strengthened a little more, to 75kts. The track has shifted towards the west over the last few forecasts as the ridge to the north of Ana has remained stronger than anticipated. Ana will still bring some adverse weather to the Hawaiian Islands, though a direct landfall is now looking less likely. Gradually increasing shear should weaken Ana over the next couple days. Thereafter, shear could ease northwest of Hawaii, though this is uncertain.

[Somerset Squall]

Moderate shear has weakened Ana slightly, to 70kts. The hurricane is passing southwest of the Hawaiian Islands, but is still bringing heavy rains to them. Ana is forecast to weaken a little more before shear eases as Ana turns to the north, which should allow some re-intensification to the northwest of Hawaii, as waters are anonmolously warm here. Ana is forecast to remain a hurricane throughout the next 5 days.

[Typhoon43]

Ana has weakened to a high-end TS. The CPHC forecast strengthening starting form 36 hours and reaching peak intensity between day 3-4.

[Somerset Squall]

Ana has been severely disrupted by shear. Convection has significantly waned, and the LLCC is completely exposed to the west of the remaining convection. Winds have fallen to 45kts. Ana should re - strengthen soon as the strong westerly shear eases, but Ana is not forecast to become a hurricane again. By day 5, as Ana recurves to the northeast, it will begin extratropical transition.

Edited October 21, 2014 by Somerset Squall

[knocker]

Quite interesting stuff on Ana.

 

GOES-15 Rapid Scan Operations imagery of Tropical Storm/Hurricane Ana (plus other satellite images) http://go.wisc.edu/rp9w85

[Somerset Squall]

11 day old Ana is still roaming the Central Pacific with 45kt winds this morning. The storm is currently moving slowly northwestward to the northwest of the Hawaiian Islands. Ana is forecast to strengthen a little as shear has lessened and the storm is over reletively warm water. Thereafter, Ana should make the long awaited turn northeast and accelerate whilst becoming extratropical. This is likely to occur in about 3 days time.

Edited October 24, 2014 by Somerset Squall

[Somerset Squall]

Ana has strengthened decently through this afternoon and evening, and looks like it could be approching hurricane intensity again. Winds are up to 55kts. Convection has blossomed over the LLCC, something which has been lacking over the last couple days. Furthermore, an eye appears to be taking shape again. Will Ana become a hurricane for the second time?

Edited October 24, 2014 by Somerset Squall

[Somerset Squall]

Ana has become a hurricane again, with winds of 65kts. At 31 degrees north, this shows how anomalously warm the waters are in Central Pacific this year, especially as we are in late October. Convection is already beginning to weaken around the eye however, so Ana will probably not remain a hurricane for long. Indeed, the northeast turn has already started, which will send Ana over progressively cooler water, and into higher shear, which will induce extratropical transition soon.

[Vorticity0123]

Long living and tenacious Ana continues to stubbornly maintain hurricane status in the central Northern Pacifc. However, signs are there that this will not last for very long. In fact, the low level circulation center (LLCC) is becoming exposed to view to the west of a weakening area of convection. This can be seen below:

 

Visible satellite image of Ana (Courtesy: NOAA). Note that the image auto-updates itself.

 

There is also a large area of stratocumulus clouds to the northwest of Ana, indicating that the air is very stable at that location.

 

As noted by Somerset Squall, Ana was moving over anomalously warm SSTS (sea surface temperatures), which have been a factor in causing Ana to retain its tropical status up to 36.5N. This is a highly unusual occurrence, but not totally unpreceded. In fact, five tropical cyclones have retained their tropical status even up to 40N¹.

 

Finally, the system can be seen from a beautful perspective by looking at imagery from the Northeastern Pacific:

 

Visible satellite image of the Northeastern Pacific (Courtesy: NOAA). Note that the image auto-updates itself.

 

According to the CPHC, Ana will also be able to make it into the list of cyclones reaching 40N latitude in the central Pacific. It will be interesting to see up to which latitude it will be able to maintain its tropical status.

 

Sources:

¹: http://en.wikipedia.org/wiki/1975_Pacific_Northwest_hurricane#cite_note-EPAC_HURDAT-4http://www.prh.noaa.gov/cphc/tcpages/archive/2014/TCDCP5.CP022014.049.1410252035

http://www.nhc.noaa.gov/satellite.php

Edited October 25, 2014 by Vorticity0123

[Somerset Squall]

After 13 days as a tropical system, Ana has finally become extratropical. It's been an interesting watch! And it could've been so much worse for Hawaii if initial forecasts verified.

Final track of Ana. Has been fairly unusual to say the least: