040813云娜
超强台风
超强台风
  • 注册日期2011-09-23
  • 最后登录2017-04-11
  • 粉丝50
  • 关注41
  • 发帖数3174
  • 来自
阅读:1506回复:1

[气象讯息]由于厄尔尼诺几率上升,CSU预计2015大西洋飓风季节是一个平静的季节

楼主#
更多 发布于:2015-04-22 10:16
CSU Predicts a Quiet 2015 Atlantic Hurricane Season Due to Rising El Niño Odds
By: Jeff Masters ,
Another quiet Atlantic hurricane season is likely in 2015, said the hurricane forecasting team of Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) in their latest seasonal forecast issued April 9. They called for an Atlantic hurricane season with 7 named storms, 3 hurricanes, 1 intense hurricane, and an Accumulated Cyclone Energy (ACE) of 40. The long-term averages for the period 1971 - 2010 were 12 named storms, 6.5 hurricanes, 2 intense hurricanes, and an ACE of 92. The 2015 forecast calls for a below-average chance of a major hurricane hitting the U.S., both along the East Coast (15% chance, 31% chance is average) and the Gulf Coast (15% chance, 30% chance is average). The Caribbean is forecast to have a 22% chance of seeing at least one major hurricane (42% is average.) Five years with similar pre-season February and March atmospheric and oceanic conditions were selected as "analogue" years that the 2015 hurricane season may resemble: 2014 (which featured 8 named storms, 6 hurricanes, and 2 intense hurricanes); 1993 (8 named storms, 6 hurricanes, and 2 intense hurricanes); 1991, featuring Hurricane Bob, which hit Long Island, New York as a Category 2 storm; 1987 (7 named storms, 3 hurricanes, and 1 intense hurricane); and 1957, which featured the deadliest June hurricane on record, Hurricane Audrey, which killed 416 people in Texas and Louisiana. These five years all had at least moderate El Niño conditions and cool Sea Surface Temperatures (SSTs) in the tropical Atlantic. The average activity for these years was 8 named storms, 4 hurricanes, and 2 major hurricanes.
Figure 1. Hurricane Gonzalo as seen from the International Space Station on October 16, 2014. At the time, Gonzalo was at peak strength, with 145 mph winds, and was the first Atlantic hurricane to reach sustained winds of at least 145 mph since Hurricane Igor of 2010. Gonzalo hit Bermuda just a week after Hurricane Fay hit the island, and Gonzalo's remnants went on to batter the United Kingdom on October 21 with wind gusts exceeding 100 mph, killing three people there. Image credit: Alexander Gerst.
Why the forecast of a quiet season?
The CSU team cited two main reasons why this may be an quiet hurricane season:1) A weak El Niño event is underway in the Eastern Pacific, and is expected to intensify by this fall (see the discussion below in this post's last paragraph.) If El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. Sea surface temperatures were 0.7°C above average over the past week in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for a weak El Niño event to be declared. By August-October, most dynamical models are calling for a moderate El Niño (Niño 3.4 temperatures at least 1.0°C above average) or strong El Niño (Niño 3.4 temperatures at least 1.5°C above average). The European Centre for Medium-Range Weather Forecasts (ECMWF) shows the best prediction skill of the various El Niño/Southern Oscillation (ENSO) models, and the average of the various ECMWF ensemble members is calling for a strong El Niño event by September (a Nino 3.4 SST anomaly of approximately 1.7°C.)2) Sea surface temperatures (SSTs) in the Main Development Region (MDR) for hurricanes from the Caribbean to the coast of Africa between 10°N and 20°N were much cooler than average in the eastern tropical Atlantic, and near average in the Caribbean in March 2015. Much of this unusual cooling was due to a persistent positive phase of the North Atlantic Oscillation (NAO) since November 2014. A positive phase of the NAO is associated with a strengthened Bermuda-Azores High and faster trade winds across the tropical Atlantic. The faster winds increase mixing of cool water to the surface. These cooler SSTs are associated with higher-than-normal sea level pressures which can create a self-enhancing feedback that relates to higher pressure, stronger trades and cooler SSTs during the hurricane season. Virtually all African tropical waves originate in the MDR, and these tropical waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely. As always, they included the standard disclaimer with any quiet hurricane season outlook:"Despite the forecast for below-average activity, coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them. They should prepare the same for every season, regardless of how much activity is predicted."
Figure 2. Departure of sea surface temperature (SST) from average for March 2015, as computed by NOAA/ESRL. SSTs in the hurricane Main Development Region (MDR) between Africa and Central America (red box) were well below average in the eastern Atlantic, and near average in the Caribbean.
How good are the April forecasts?
April forecasts of hurricane season activity are low-skill, since they must deal with the so-called "predictability barrier." April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season. Correctly predicting this is key, since if El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due on Monday, June 1, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years. NOAA issues its first seasonal hurricane forecast for 2015 on May 27.
TSR also predicts a below-average Atlantic hurricane season
The April 9 forecast for the 2015 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) also calls for a quiet season, but is not as low as CSU's forecast. TSR is calling for 11 named storms, 5 hurricanes, 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 56. The long-term averages for the past 65 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 102. TSR rates their skill level as low for these April forecasts--just 12 - 20% higher than a "no-skill" forecast made using climatology. TSR predicts a 25% chance that U.S. landfalling activity will be above average, a 25% chance it will be near average, and a 50% chance it will be below average. They project that 2 named storms will hit the U.S., with 1 of these being a hurricane. The averages from the 1950-2014 climatology are 3 named storms and 1 hurricane. They rate their skill at making these April forecasts for U.S. landfalls just 4 - 7% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1 named storms and no hurricanes. Climatology is 1 named storm and less than 0.5 hurricanes.TSR’s two predictors for their statistical model are the forecast July - September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August - September sea surface temperatures in the tropical North Atlantic. Their model is calling for cooler than average SSTs and faster than average trade winds during these periods, and both of these factors should act to decrease hurricane and tropical storm activity. Unlike CSU, TSR is not calling for an El Niño event this fall, which is giving them higher levels of activity in the Atlantic. They add: "Should the TSR forecast for 2015 verify it would mean that the ACE total for 2013-2015 was easily the lowest 3-year total since 1992-1994 and it would imply that the active phase of Atlantic hurricane activity which began in 1995 has likely ended." The next TSR forecast will be issued on May 27.
WSI predicts a quiet Atlantic hurricane season
The April 13 forecast from the private weather firm WSI (part of The Weather Company, along with The Weather Channel, Weather Central, and The Weather Underground), is calling for a quiet Atlantic hurricane season with 9 named storms, 5 hurricanes, and 1 intense hurricane. WSi cites the expectation of El Niño conditions to be present this fall as the reason for reducing their expected Atlantic hurricane season numbers from last month's forecast, which called for 10 named storms, 5 hurricanes, and 2 intense hurricanes.
NOAA increases El Niño odds to 60% for the fall
NOAA's monthly El Niño update issued on April 9 gives increased odds that the current weak El Niño event in the equatorial Eastern Pacific will stick around into fall. NOAA is now giving a 70% chance of El Niño lasting through summer, up from their 50 - 60% odds they gave a month ago. They give a 60% chance that El Niño will last though the fall. However, in a March 31 update, the Australian Bureau of Meteorology (BOM) cautioned: “Model outlooks spanning February to May . . . have lower confidence than forecasts made at other times of year. Some models currently show some spread in their outlooks for tropical Pacific Ocean temperatures, indicating that while further warming is indeed very likely, there remains some ambiguity about the amount of warming expected.” In hisApril 9 post, Wunderblogger Steve Gregory gave a 70% El Niño continuing into this winter, with a 30% chance that we would see a strong El Niño event.
[040813云娜于2015-04-22 10:30编辑了帖子]
喜欢0 评分0
帖子中涉及地图来源广泛,图中所涉及的行政区域以中国官方认定的为准。
风王2012
资深会员-热带辐合带
资深会员-热带辐合带
  • 注册日期2013-11-09
  • 最后登录2017-05-22
  • 粉丝134
  • 关注71
  • 发帖数5142
  • 来自
1楼#
发布于:2015-08-20 15:05
译序:无意中翻到此贴,也想要看看美国方面每年的年度预测大概在说些什么,所以翻译- -。原则上为意译,部分内容无法理解则退而求其次直译(已注明)。由于对美国方面的气象专有名词不甚了解,可能有疏漏,欢迎指正。

由于厄尔尼诺发生的几率上升,CSU预测2015年大西洋飓风季将会是平静的
By: Jeff Masters
“2015年将很有可能是一个平静的飓风季节。美国科罗拉多州立大学(CSU)Phil Klotzbach博士和Bill Gray博士的团队在4月9日发布的飓风季最新预测中如上说道。他们认为2015年大西洋飓风季将出现七个命名风暴,三个飓风,一个强烈飓风和一个气旋累计能量(ACE)为40的飓风。1971年-2012年长期以来的平均值是:每年出现十二个命名风暴,6.5个飓风,两个强烈飓风和一个气旋累计能量为92的飓风。而且,他们预测2015年飓风季将有一个飓风袭击美国,这低于历史平均水平。美国东海岸(15%的可能,历史平均水平为31%)-墨西哥湾沿海(15%的可能,历史平均水平为30%)均有可能。(他们)预测加勒比地区将有22%的机会出现至少一个大型飓风(历史平均水平为42%)。一共有5个年份被认为于2015年2月、3月的大气环境条件类似:2014年(共出现八个命名风暴,六个飓风和两个强烈飓风);1993年(共出现八个命名风暴,六个飓风和两个强烈飓风);1991年(该飓风季中的飓风Bob,以二级飓风的强度影响了纽约长岛);1987年(共出现七个命名风暴,三个飓风和一个强烈飓风)和1957年(该飓风季中的飓风Audrey为6月最致命的飓风,在德克萨斯州和路易斯安那州造成了416人死亡)。这五个年份都至少出现了中等厄尔尼诺,大西洋的海温偏低的现象。这些年份平均出现了八个命名风暴,四个飓风和两个大型飓风。

图片:gonzalo-iss-oct16.jpg


图片1   2014年10月16日从国际空间站中拍摄的飓风Gonzalo。当时,其正达到巅峰强度145英里/每小时(约65m/s,笔者注),它也是自2010年飓风Igor后首个风速达到145英里/每小时以上的飓风。飓风Gonzalo在飓风Fay吹袭百慕大群岛仅仅一周后再次吹袭该(群)岛。不仅如此,10月21日,飓风Gonzalo的残余云系带着100英里/每小时(约45m/s,笔者注)的阵风吹袭英国,并造成当地三人死亡。图片来源:Alexander Gerst

为什么预测这将是一个平静的飓风季?
CSU团队援引了两个他们认为这将是一个平静的飓风季的原因:
1)一次较弱的ENSO现象正在东太平洋进行中,他们预测这一次厄尔尼诺现象将在今年秋天加剧(可参见本文最后一段的讨论)。如果ENSO事件将持续至今年秋天,那么它将在大西洋的高空创造出大量的垂直风切变并切离热带气旋的对流从而带来一个平静的飓风季。在Nino3.4(5°S - 5°N, 120°W - 170°W)海温在过去一周内比平均值高0.7℃。当该地区连续五月海温距平保持在0.5℃以上(每一个月计算过去三个月的海温平均值)时,即可认定这是一次弱厄尔尼诺现象。大多数的动力模型已经预测出这将是一次中等厄尔尼诺现象(Nino3.4区连续五月海温距平保持在1.0℃以上)甚至强厄尔尼诺现象(Nino3.4区连续五月海温距平保持在1.5℃以上)。欧洲中期天气预报中心拥有预测厄尔尼诺准确度最高的模型,他们的集合预报显示这将是一次强厄尔尼诺现象(Nino3.4区连续五月海温距平保持在1.7℃以上)。
2)在大西洋热带气旋的主要生成地区(MDR)(位于加勒比海-非洲东海岸之间10°N-20°N的海域)的海温将比2015年3月和大西洋上其他地方更低。这次不同寻常的海温偏低主要是因为从2014年11月持续至今的北大西洋震荡(NAO)。正处于活跃状态的NAO被证明与加快百慕大群岛-亚速尔群岛信风通过大西洋的速度有联系,而低海温则被证明与更高的海平面气压有关系,这种增强反馈机制将导致出现更高的海平面气压、更强的信风和更低的海温。而几乎所有的非洲热带波动都起源于该主要生成地区,这些非洲热带波动为85%大型飓风和60%命名风暴的前身。当主要生成地区的海温远高于平均水平时,通常都会该飓风季非常活跃(前提是没有出现厄尔尼诺事件)。相反,当主要生成地区的海温低于平均水平时,该飓风季平静的可能性会更大。
一如既往地,他们还是打出了和所有预测将平静的飓风季前预报一样标准的免责声明:“尽管预报将出现一个平静的飓风季,但我们提醒沿海居民,只需要一个飓风登陆就可以使这个飓风季变得活跃(这段话语义不详,为直译),但不管预测有多少个飓风活动,(沿海居民)仍然应当像往年一样做好准备。

图片:sst-mar2015.png


图片2   2015年三月海温距平图,来自NOAA/ESRL,主要生成地区在图中非洲东海岸-中美洲之间的海域,也就是红框内。其中东大西洋海温远低于平均水平,加勒比海海温略低于平均水平。

四月的预测有多准?
四月就对全年的热带气旋进行预测是项低技术含量的活儿,因为他们必须考虑所谓的“可预测性障碍”。四月是一年中厄尔尼诺现象变化较快的一年,常常从一个状态转变为另一种状态,因而我们很难预测厄尔尼诺现象会否出现,是否成为即将到来的的飓风季的中性影响条件。准确预测最关键,因为如果厄尔尼诺事件将持续至今年秋天,那么它将在大西洋的高空创造出大量的垂直风切变并切离热带气旋的对流从而带来一个平静的飓风季。就现在而言,四月的预测应当仅仅看做是一项有趣的研究工作,而且有潜力成为精准度更高的预测。下一份CSU报告将于6月1日星期一发布,这份报告值得关注。6月初的预报将展示该预报机构的预报能力。NOAA则将在5月27日发表对首份对2015年飓风季的预测。

TSR也预测2015年大西洋飓风季较往年相比更平静
英国气旋风险私人预测公司(TSR)于4月9日发表的预测也认为2015年大西洋飓风季较往年相比更平静,但并不像CSU团队预测那般平静。TSR认为2015年大西洋飓风季将出现十一个命名风暴,六个飓风,三个猛烈飓风和一个累计气旋能量(ACE)达到56的飓风。过去六十五年以来的平均值是:每年出现十一个命名风暴,六个飓风,三个强烈飓风和一个气旋累计能量为102的飓风。TSR认为他们的四月预测能力较低——只比不采用气候学的预测准确度高12%-20%,TSR也认为有25%的机会登陆美国的热带气旋数量高于平均水平,25%的机会登陆美国的热带气旋数量与常年同期持平,50%的机会登陆美国的热带气旋数量低于平均水平。根据他们的预测,将会有两个命名风暴吹袭美国,其中包括一个飓风。1950年-2014年的气候学平均水平是每年有三个命名风暴,其中包括一个飓风吹袭美国。TSR认为他们在四月对美国热带气旋的预测能力较低——只比不采用气候学的预测准确度高4%-7%。根据他们的预测,将会有一个命名风暴吹袭加勒比海上的小安的列斯群岛,其中没有飓风。气候学平均水平是每年有一个命名风暴和少于0.5个飓风吹袭小安的列斯群岛。TSR的两个主要预测因子是7月-9月北大西洋-加勒比海的信风风速和8月-9月北大西洋海温,他们的模型预测结果是:海温比平均水平低,信风风速比平均水平快。这两个关键因素都将抑制热带气旋的发展。于CSU团队不同,TSR并不认为厄尔尼诺事件将持续至今年秋天,这是TSR给出的预测比CSU团队给出的预测更活跃的原因。他们还补充道:“根据我们对2015年大西洋飓风季的预测,2013年-2015年的ACE总数将轻而易举地低过1992年-1994年的ACE总数。这意味着于1995年开始的北大西洋飓风活跃期可能已经结束了。”下一份TSR预测将于5月27日发布。


WSI也预测2015年大西洋飓风季较往年相比更平静
4月13日由私人天气公司WSI(一个天气公司,与天气频道、气象中心、地下气象台打交道)发布的报告也预报出了一个平静的飓风季,他们预测2015年飓风季将出现九个命名风暴,五个飓风和一个猛烈飓风。WSI援引“厄尔尼诺现象将持续至秋天”作为减少他们上个月预测数字的原因,当时他们预测将会出现十个命名风暴,五个飓风和两个猛烈飓风。


NOAA将厄尔尼诺现象持续至秋天的可能性提升至60%
NOAA于4月9日发布的厄尔尼诺更新报告提升了厄尔尼诺现象持续至秋天的可能性。NOAA现在对厄尔尼诺现象持续至夏天给出70%的可能性,这比他们上个月给出的50%-60%要高,并对持续至秋天的可能性提升为60%。而在澳大利亚气象局(BOM)于3月31日发布的报告警告说:“当前模型认为厄尔尼诺现象将跨越2月-5月,我们对此的信心低于一年中其他预测时段(这段话语义不详,为直译)。一些模型最近表明热带太平洋海温上升可能性确实存在,很大一部分模型对是否升温态度不明显。”在4月9日发表的邮件中,Steve Gregory认为厄尔尼诺现象将持续至冬天有70%的可能性,而且这是一次强厄尔尼诺事件的可能性为30%。
[风王2012于2015-08-21 16:27编辑了帖子]
3条评分, 贡献值 +10 好评度 +5
我们相识在冬季。
回复(0) 喜欢(0)     评分(3)
游客

返回顶部