北大西洋61年來一月最強颶風「海溫20℃」 - 颱風討論

大家好我是K.Richard 鬆々
初次發文之前都在潛水XD

在昨天由溫帶氣旋變性為副熱帶氣旋的Alex，
昨天一整天幾乎都有著相當清晰的風眼，
在稍早更得到了暖心結構，變性為一級颶風，
風速提升至75節，
成為北大西洋1955年以來，
一月最強的颶風，
並且預測最大風速仍有再增強至80節之機會，
若成真將會並列1955年Alice颶風成為北大西洋一月史上最強颶風之一。

更特別的是這颶風所處在的海溫，
只有攝氏約「20度C」，
完全顛覆了教科書上，
海溫必須達到24~26度C以上才能夠支持一個熱帶氣旋發展的說法，
是一個「非常」特殊的案例。

在這裡想跟大家討論，
究竟是什麼機制讓這個颶風再如此低的海溫下，
還能夠繼續增強甚至發展出如此完整的風眼結構？

以下是這個颶風的相相關資料與圖片...

MODIS - Terra 高解析影像
http://i.imgur.com/aAzQ0Yp.jpg

NRL -IR-Color 2016.01.16 1515Z UTC
http://i.imgur.com/RBw5Kab.jpg

OHC = "0"
http://i.imgur.com/cYYeYpT.gif

SST 約20℃左右
http://i.imgur.com/OyaYntu.png

NHC路徑預測圖
http://i.imgur.com/VKyccpn.gif

NHC文字報告
000
WTNT41 KNHC 141434
TCDAT1

HURRICANE ALEX DISCUSSION NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL AL012016
1100 AM AST THU JAN 14 2016

Remarkably, Alex has undergone the transformation into a hurricane.
A distinct eye is present, embedded within a fairly symmetric mass
of deep convection. Water vapor imagery shows that the upper-level
trough is now west of the cyclone, with divergent flow over the
center - indicative of a tropical transition. It is very unusual to
have a hurricane over waters that are near 20 deg C, but the
upper-tropospheric temperatures are estimated to be around -60 deg
C, which is significantly colder than the tropical mean. The
resulting instability is likely the main factor contributing to the
tropical transition and intensification of Alex. With these
changes, the government of the Azores has issued warnings for most
of the Azores islands.

The initial intensity is set to 75 kt in accordance with the
analyzed Dvorak T-number of 4.5. Only slight additional
intensification seems possible since the system will be passing
over even colder waters during the next day or two. In 36 hours,
the global models suggest that the cyclone will become
extratropical as it begins to merge with a large low pressure area
at high latitude. The post-tropical cyclone is then likely to lose
its identity after 48 hours.

The initial motion is north-northeastward or 020/17 kt. Alex is
being steered by a shortwave mid-level trough that is rotating
around a larger trough to the northwest. This should cause the
cyclone to turn northward and north-northwestward and accelerate
over the next couple of days. The official track forecast is very
similar to the previous one and also quite close to the consensus
of the tightly-packed dynamical model forecast tracks.

Alex is the first hurricane to form in the month of January since
1938, and the first hurricane to occur in this month since Alice of
1955.

FORECAST POSITIONS AND MAX WINDS

INIT 14/1500Z 31.5N 28.4W 75 KT 85 MPH
12H 15/0000Z 34.3N 27.7W 80 KT 90 MPH
24H 15/1200Z 38.9N 27.7W 75 KT 85 MPH
36H 16/0000Z 45.3N 28.6W 60 KT 70 MPH...POST-TROP/EXTRATROP
48H 16/1200Z 53.0N 31.5W 60 KT 70 MPH...POST-TROP/EXTRATROP
72H 17/1200Z...DISSIPATED

$$
Forecaster Pasch

總而言之，太神啦~~~

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