Hurricane Irma Discussion Number 44 - 颱風討論

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WTNT41 KNHC 100258
TCDAT1

Hurricane Irma Discussion Number 44
NWS National Hurricane Center Miami FL AL112017
1100 PM EDT Sat Sep 09 2017

Irma's nearly 24-hour traversal of the north coast of Cuba appears
to have affected the hurricane's structure and intensity. An
earlier NOAA Hurricane Hunter aircraft and a more recent Air Force
reconnaissance flight both measured maximum flight-level winds near
105 kt and surface winds near 95 kt. The planes have reported
a double eyewall structure, which has also been observed in WSR-88D
Doppler radar data from Miami and Key West. Irma's intensity has
been conservatively lowered to 105 kt, and I'd rather wait to lower
the winds further until we've seen the full data set from the Air
Force mission.

Irma在古巴幾乎二十四小時的旅程顯示出已經影響到颶風的結構與強度
稍早一架NOAA颶風獵人機與最新的空軍機偵查飛行一起測量得出近105節最大飛行高度風
以及近95節表面風力.
兩機均回報發現雙眼牆結構, 此結構也在西礁島群與邁阿密的WSR-88D雷達觀測到
Irma的強度已經保守地降低到105節, 我寧願等著更加降低風力, 直到我們已收到空軍機
完整的數據集

Irma has stuttered near the north coast of Cuba for the past few
hours, which may be a harbinger of the north-northwestward turn
that we've been waiting for. In any event, Irma appears to be
moving very slowly toward the northwest, or 305/5 kt, very gradually
shifting away from the north coast of Cuba. With the hurricane
located near a break in the subtropical ridge, it should turn
north-northwestward soon and accelerate near or along the west
coast of Florida during the next 36-48 hours. Because of Irma's
hesitation to move northwestward, the new track guidance has shifted
ever so slightly westward, and the new NHC track is just a little
left of the previous one. Although it is likely that the eye will
move near or over the Lower Keys Sunday morning, the hurricane's
angle of approach to the west coast of Florida makes it very
difficult to pinpoint exactly where Irma will cross the Florida Gulf
coast.

Irma在過去數小時來時斷時繼地在古巴北部的海岸附近, 這可能是我們一直在等待的北北
西轉向的預兆。
無論如何, Irma顯示似乎緩慢地以305度5節向西北方向移動, 非常緩慢地從古巴北部海岸
轉離
隨著颶風位於副熱帶高壓脊缺口附近, 這應該在接下來三十六到四十八小時內快速轉向
北北西, 並在佛州西海岸附近或是沿著西海岸加速移動
由於伊爾瑪猶豫不決地向西北移動, 新的路徑指導已經向西移動一點, 本局新的路徑只比
前一報向左一點
雖然風眼可能將在週日早晨接近或是穿越下礁島群, 但颶風向佛州西海岸的接近角度造成
很難確實定位Irma會在佛州彎曲海岸的何處通過

If an eyewall replacement occurs within the next 6-12 hours, Irma
has an opportunity to restrengthen a bit while it moves across the
Straits of Florida. After that time, however, southwesterly shear
is expected to increase to 25-30 kt in about 24 hours and then
continue increasing through 48 hours. This shear, in addition to
Irma's core interacting with Florida, is likely to cause a
weakening trend after 24 hours. The new intensity guidance calls
for an adjustment from the previous forecast, although it
conservatively lies near the upper bound of the reliable models.
Irma is still expected to approach the Florida Keys and Florida
west coast as a major hurricane, and combined with its large size,
will produce significant storm surge flooding in those areas.

如果在接下來六到十二小時內發生眼牆置換, 當Irma通過佛州海峽時有稍微增強的機會
此時之後, 西南向風切預料約在二十四小時時增加到25-30節,
接著直到四十八小時持續增強.
此風切加上Irma核心與佛州陸地交互作用, 有可能會在二十四小時後出現減弱趨勢
新強度指引提出對前一報的修正, 雖然這保守地落在數值預報中可信度的上限
Irma依然預計以主要颶風接近佛州礁島群與佛州西海岸,
結合颶風本身巨大的尺寸,這將會以上地區產生顯著的風暴潮溢洪


KEY MESSAGES:

1. Irma is expected bring life-threatening wind and storm surge to
the Florida Keys and southwestern Florida as an extremely dangerous
major hurricane tonight through Sunday. Preparations in the Florida
Keys and southwest Florida should be complete since tropical-storm-
force winds are already affecting portions of the coast.

2. There is an imminent danger of life-threatening storm surge
flooding in portions of central and southern Florida, including the
Florida Keys, where a Storm Surge Warning is in effect. The threat
of catastrophic storm surge flooding is highest along the southwest
coast of Florida, where 10 to 15 feet of inundation above ground
level is expected. This is a life-threatening situation, and
everyone in these areas should immediately follow any evacuation
instructions from local officials.

3. Irma will bring life-threatening wind impacts to much of Florida
regardless of the exact track of the center. Wind hazards from Irma
are also expected to spread northward through much of Georgia
and portions of South Carolina and Alabama.

4. Irma is expected to produce very heavy rain and inland flooding.
Total rain accumulations of 10 to 20 inches, with isolated amounts
of between 20 and 25 inches, are expected over the Florida Keys, the
Florida peninsula, and southeast Georgia from Saturday through
Monday. Significant river flooding is possible in these areas. Early
next week Irma will also bring periods of heavy rain to much of the
southeast United States where an average of 2 to 6 inches is
forecast, with isolated higher amounts, from North and South
Carolina to Tennessee and eastern Alabama. This includes some
mountainous areas which are more prone to flash flooding. Residents
throughout the southeast states should remain aware of the flood
threat and stay tuned to forecasts and warnings.

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