REVIEW OF THE PAST HURRICANE SEASON

Transcription

1 WORLD METEOROLOGICAL ORGANIZATION RA IV HURRICANE COMMITTEE THIRTY-FIFTH MEETING RA IV/HC-35/Doc. 4.2(9) (03.IV.2013) ITEM 4.2 WILLEMSTAD, CURACAO 8 12 APRIL 2013 ENGLISH ONLY REVIEW OF THE PAST HURRICANE SEASON Reports on hurricanes, tropical storms, tropical disturbances and flooding associated with those events occurring in 2012 Report of Bermuda (Presented by Bermuda)

2 Table of Contents Review of 2012 Season... 1 Hurricane Chris, June 18 th 22 nd... 1 Tropical Storm Debby, June 23 rd 28 th... 2 Hurricane Leslie, August 30 th September 11 th... 2 Hurricane Rafael, October 12 th 17 th... 3 Hurricane Sandy, October 22 nd to 29 th... 4 Summary Table Tropical systems that affected Bermuda... 7 Review of 2012 Season Bermuda was affected to varying degrees by a total of 5 separate systems during the 2012 season. These included Hurricane Chris, Tropical Storm Debby, Hurricane Leslie, Hurricane Raphael and Major Hurricane Sandy (N.B. the status of these cyclones is the maximum intensity during the lifecycle of the cyclone, and not necessarily the intensity as the cyclone affected the Bermuda area). This made it a busy season for BWS, with Hurricane Chris developing near the start of the season on June 18 th, and Hurricane Sandy affecting us towards the end of the season in late October. The most significant impacts to the Island were felt from Leslie, Rafael and Sandy. Hurricane Chris, June 18 th 22 nd An area of low pressure developed over the Island during June 17 th. Please see the 1352Z Ascat pass and subsequent 1622Z Oscat pass below: This would eventually become Tropical Storm Chris on June 19 th (NHC advisory #1 issued at 6pm) by then well to our northeast. It even managed to gain weak category 1 hurricane status on the 21 st. Despite the undeveloped nature of the Chris over the Island on the 17 th, it still managed to produce a spell of gale force winds with storm force gusts (due to significant mesoscale effects around the centre Author: KIMBERLEY ZUILL/ JAMES DODGSON Page 1 3/28/2013

3 of the low see previous Oscat pass for details). Some heavy rainfall also fell, accumulating to The maximum sustained winds were 40 knots with a gust to 56 knots. BWS issued a Severe Weather Warning as well as a Gale Warning. No tropical watches or warnings were issued for Bermuda in association with Chris due to the system not gaining tropical characteristics until past the area on the 19 th June). Tropical Storm Debby, June 23 rd 28 th As of 12am local time on Wednesday 27 th June (NHC advisory #15), Bermuda was under Potential Threat status for Tropical Depression Debby strengthening back into a Tropical Storm over the west Atlantic (off Florida), and possibly affecting Bermuda over the weekend of the 30 th June and 1 st July, as it moved by northeast of the Island. However, Tropical Depression Debby did not re-strengthened into a Tropical Storm, and instead weakened further to a Post Tropical Cyclone north of the Bahamas later that same day with the final advisory #18 being issued at 6pm. In advance of weakening Debby, the Island recorded mean winds of 25 knots on the 27 th, with gusts to 37 knots. There was a modest amount of moisture associated with post tropical cyclone Debby as it eventually passed by to the north of Bermuda later on the 29 th giving 0.81 of rainfall over a 3 day period. Despite Debby being a potential threat to the Island for a time, it weakened before BWS had to consider issuing any tropical watches or warnings. Hurricane Leslie, August 30 th September 11 th This was arguably the most significant tropical cyclone of the season to affect Bermuda, with Tropical Storm conditions impacting the Island (both tropical storm force winds and very rough to high seas/swells) on the 9 th September as it moved by to our near east (around 100nm) as a strong tropical storm during the morning. See the following Ascat pass and RADAR image: Leslie was a very difficult cyclone to forecast, not only in terms of intensity, but also with regards to precise track, due to significant stalling of the system around nm to the south-southeast of Bermuda over a period spanning September 3 rd through the 7 th. It originated as an area of low pressure in the deep tropical Atlantic, and had much the same characteristics as a Cape-Verde type storm. Mean winds peaked at 35 knots with gusts to 48 knots at Author: KIMBERLEY ZUILL/ JAMES DODGSON Page 2 3/28/2013

4 L.F. Wade International Airport where as the more exposed location of Commissioner s Point in Dockyard recorded gusts to near hurricane force strength (63 knots). As Leslie exited northeast on the 10 th maximum sustained wind speeds of 28 knots and gusts to 38 knots were recorded. Leslie was a significant rainmaker for Bermuda, with the western cloud shield of the cyclone moving over the Island, bringing copious amounts of rain fell on the 9 th - this registered as Bermuda s wettest day in several years. (See radar swath above). BWS issued a Tropical Storm Watch at 6pm on September 6 th, as per the NHC advisory #30. This was upgraded to a Tropical Storm Warning at 6am September 8 th, as per NHC advisory #36. All tropical warnings were dropped by 12am on September 10 th, as per advisory #43. Note that the issued warnings generally verified well with observed conditions, once they finally started affecting the island. Socio-economic impacts of Leslie included close to a thousand power outages across the Island, as well as almost complete cancellation of flight operations at L F Wade International Airport on the 9 th, with the exception of British Airways during the evening. Some minor infrastructure damage were reported a street pole in Hamilton while scattered tree branch debris and localised flooding was also observed. Further to these, it must be noted that the local EMO requested a meeting when the tropical system was forecast to increase to a Cat 2 Hurricane with a direct hit in 5 days. Based on Advisory #25, BWS director Kimberley Zuill, communicated the complications and the uncertainty, emphasizing that the advisory called for a Cat 2 to pass very slowly, directly over the island over a weekend (when media broadcasts are few & the EMO rarely meets), however there was also a possibility that Leslie could behave more like a Bertha -2008, which became disengaged from the upper level flow and sat fairly stationary to our south resulting in very slow and erratic forward movement. Regardless, the EMO was keen to initiate preparations as if the direct hit was inevitable. By the next EMO briefing a couple of days later, when Leslie was understood to not be strengthening as advisory #25 indicated, instead behaving similar to Bertha-2008, and then passing to the east as a tropical storm, the EMO hesitated on calling off preparations due to the weekend passage and forecast uncertainty. This action was preemptive, however costly, in both time and lost wages, as well as public confidence, as it came across as the storm that didn t in the eyes of the public. This attitude becomes challenging to overcome with subsequent systems, and it is a problem that not only Bermuda faces, but with the higher frequency of near misses, it is hard to raise the public out of the drone of complacency. Also, it is a challenge to convince the EMO not to lead with statements such as this tropical system is just like a winter blow. BWS continues to communicate the uncertainty of the track and especially the intensity forecasts in a realistic manner. Hurricane Rafael, October 12 th 17 th Rafael developed from a tropical wave, becoming a tropical storm near St Lucia during the evening of the 12 th, thanks to reconnaissance from the Hurricane Hunters. It was then upgraded to a moderate category 1 hurricane several hundred miles north of Puerto Rico at 9pm on the 15 th (NHC advisory #13A). Despite passing Bermuda around 95nm to the east as a moderate category 1 hurricane during the evening of Tuesday 16 th (with a Tropical Storm Warning in force for Bermuda) Rafael did not have as significant impact on the Island as Leslie. It was also a lot more predictable in nature, regarding Author: KIMBERLEY ZUILL/ JAMES DODGSON Page 3 3/28/2013

5 track and intensity. Conditions in Bermuda deteriorated quite quickly on the 16 th as it moved towards our near east from the south see the 1350Z Ascat pass below: Mean winds at the airport peaked at 31 knots, while gusts reached as high as 45 knots. The more exposed location of Commissioner s Point (especially to northeasterly winds) recorded 45 knot means with gusts to 55 knots out of the northeast. A notable amount of rainfall was associated with the passage of Rafael, with the airport recording Several hundred power outages were reported, while some disruption to flight at L F Wade International airport occurred not as widely as during Leslie though. BWS issued a Tropical Storm Watch at 12pm on the 14 th (as per NHC advisory #8). This was upgraded to a Tropical Storm Warning at 12pm on the 15 th (NHC advisory #12). As Rafael passed by to the east, the Tropical Storm Warning was discontinued at 12am on the 17 th (advisory #18). Hurricane Sandy, October 22 nd to 29 th Hurricane Sandy was another challenging cyclone to forecast, especially in the early stages, as it tracked north across Jamaica, Cuba and then across the Bahamas (October 23 rd to 26 th ). Early model indications (especially GFS) and NHC guidance took Sandy on a northern track through the Bahamas, before steering it northeast towards the near north of Bermuda, around the sub-tropical high. However, as time progressed, the forecast track took a veer off that northeastward track, taking Sandy north then northwest, away from Bermuda and more towards the US. By this stage the model consensus was heavily weighted towards the ECMWF model, which had consistently steered Sandy away from Bermuda and more towards the mid-atlantic US coastline. Despite a steer away from Bermuda in the forecast track, the increasing and unusually large size of the cyclone, due to significant mid-latitude interactions, still meant Sandy s influence would be felt across Bermuda (as shown on subsequent wind derived satellite passes on next page). With regards to local tropical watches and warnings, BWS issued a Tropical Storm Watch at noon local time on Friday 26 th October (NHC advisory #17). The centre of Sandy was approximately 715nm westsouthwest of the Island at this time, about 20nm north-northeast of Great Abaco Island, Bahamas. This watch was then upgraded to a Tropical Storm Warning at 6pm local time on Saturday 27 th October (NHC advisory #22).The first effects on the Island were building swells from the west and a steady strengthening of winds from the morning of Friday 26 th October. Author: KIMBERLEY ZUILL/ JAMES DODGSON Page 4 3/28/2013

6 A swath of stronger winds (>15kt) passed through Bermuda on the morning of the 26 th, before a slight lull (<15kt) developed into the afternoon. Thereafter, a steady increase in winds was recorded into the 27 th. Heading into the 28 th, the strongest winds were recorded and indeed lowest pressure, as Sandy bypassed to our west, over 300nm away. What can be gleaned from these passes is that Bermuda experience spokes of stronger wind which circulated around the centre of Sandy, resulting in not a simple steady increase in wind, but rather, occasional increases, followed by occasional lulls. This variability in the winds was somewhat coincident with satellite/radar signatures too and proved to be quite a forecasting challenge for the Bermuda Weather Service, in terms of getting the right message across to the community and maintaining public confidence in our forecast. 02Z Ascat (10pm local) 29 Oct Z OSat (midnight local) 30 Oct 2012 Author: KIMBERLEY ZUILL/ JAMES DODGSON Page 5 3/28/2013

7 However, during Sunday 28 th through the early hours of Monday 29 th, some significant wind and weather was observed. A confirmed Tornado affected a part of the Somerset Village area during the morning of Sunday 28 th, at around 830am local. An extensive account of this tornado can be found in the following media report, which quotes the director of the Bermuda Weather Service, Kimberley Zuill: Please note, however, that there is one misquote in this report. Instead of the tornado being reported as barely a F1 it should read barely a F0. There is also some footage of the tornado at the following link: As for other aspects of the local weather, frequent TCu s and CB s were reported with some heavy rain showers and thunderstorms, especially during Sunday 28 th. The Tropical Storm Warning was finally dropped at 12 noon local time on Monday 29 th October as Sandy maintained a west-northwestward track towards the mid-atlantic US coast. With regards to specifics of winds and pressure, strongest winds at the airport (recorded by our Vaisala MIDAS IV airfield anemometers) were 32 knots with gusts to as high as 50 knots on the 28 th. Into Monday 29 th, winds were still peaking at 30 knots with gusts to 40 knots. The strongest official wind reading was at an automated weather station at the west end of the Island (quite an exposed site at an elevation of 150 feet). The anemometer at Commissioner s Point in Dockyard recorded a mean wind speed of 35.1 knots at 0050Z on the 29 th (850pm local time during the evening of Sunday 28 th ), while a gust of 50.9 knots was recorded at the same location at 0340Z on the 29 th (1140pm local time on the 28 th ). Another exposed site in St George s at the east end of the Island (Marine Operations Centre, also known as Harbour Radio, sited at the old Fort St George) is likely to have recorded some of the most Author: KIMBERLEY ZUILL/ JAMES DODGSON Page 6 3/28/2013

8 extreme wind speeds, but this data is still being sourced. The anemometer there is at an elevation or roughly 250ft. Once the data is available, this detail will be forwarded. With regards to pressure, our MIDAS IV airfield equipment reported a lowest mean sea level pressure of 994.8mb, while an in house Meteograph trace recorded a touch lower at 994.4mb. This was at approximately 0320Z on the 29 th (1120pm local time on Sunday evening, the 28 th ). The calendar year of 2012 recorded only 2 other pressure reading this low (with very similar values: mb). The first was in late March associated with a late wintertime mid-latitude low pressure system, the second associated with the passage of Hurricane Rafael to our east a couple of weeks prior to Sandy. Finally, the Tropical Storm Warning for Bermuda was discontinued at 12 noon on Monday 29 th October (NHC advisory #29). Summary Table Tropical systems that affected Bermuda Summary Table Storm Month Watch/Warning Issued for Bermuda Hurricane Chris (pre-development) TS Debby (posttropical) June Severe Weather Warning, Gale Warning Maximum Wind Speed at LF Wade 40 knots gust 56 June Small Craft Warning 25 knots gust 37 Hurricane Leslie (as a Tropical Storm) September TS Watch, TS Warning Hurricane Rafael September TS Watch, TS Warning Category 3 Hurricane October TS Watch, TS Sandy (as a Cat 1 Warning Hurricane) 35 knots gust knots gust knots gust 50 Author: KIMBERLEY ZUILL/ JAMES DODGSON Page 7 3/28/2013