WORLD METEOROLOGICAL ORGANIZATION
___________________________________________
RA IV HURRICANE COMMITTEE
RA IV/HC-XXXIII/Doc. 4.2(3)
(03.II.2011)
________
THIRTY-THIRD SESSION
ITEM 4.2
GRAND CAYMAN, CAYMAN ISLANDS
8 TO 12 MARCH 2011
Original: ENGLISH
REVIEW OF THE PAST HURRICANE SEASON
REPORTS OF HURRICANES, TROPICAL STORMS, TROPICAL
DISTURBANCES AND RELATED FLOODING DURING 2010
(Submitted by Bermuda )
1.
INTRODUCTION
The 2010 Atlantic Hurricane Season was one in which 5 storms threatened the island,
with one (Igor) making a significant impact, whilst the others either dissipated nearby or veered
away ‘on the doorstep’. This meant a few challenges in operations and maintaining a level of
credibility in the eyes of the public. However, with our one impact this year, Bermuda benefited
from a heightened sense of preparedness in advance of the onset of damaging conditions.
Thankfully, no injuries or losses of life were reported this hurricane season, and only minimal
impacts to property and infrastructure were evident. The four systems which came close, but
produced minor impacts, are summarized below, whilst Hurricane Igor is described in more
detail in the next section.
1.1
Tropical Storm Colin
A Tropical Storm Warning was posted at 11:30am on Thursday 6 August, in anticipation
of Colin producing winds in excess of 34 knot at times on the following weekend. However, the
only real impact of Colin was building seas and swells on the South Shore. TS Colin continued
to weaken through Saturday 7 August, with only a few bands of showers and one thunderstorm
affecting the area. Seas and swells continued to build from the south, though area winds
averaged 25 knots as Colin's slowing continued to delay the onset of tropical storm force winds,
which had been forecast for the weekend from as early as Thursday. At noon on Sunday 8
August Colin was downgraded to a tropical depression and was declared “dissipated” at 6pm.
As Colin continued to weaken, it produced maximum sustained winds of 28 knots with a peak
gust of 40 knots at the Commissioner’s Point AWOS site at 18:30 UTC on 8 August (for
metadata on this AWOS site, see item 2.3).
1.2
Hurricane Danielle
Hurricane Danielle, a late August major hurricane, was never forecast to come close
enough to Bermuda to even produce tropical storm force winds, let alone hurricane force winds.
However, Danielle was treated with caution, as the position and direction of the system’s
movement meant hat large swells were forecast for the south shore beaches. This prompted a
Small Craft Warning to be posted and a Tropical Storm Watch was also issued on the 27
August to cover the unlikely eventuality that Danielle’s peripheral winds would skirt our Marine
Area (in addition to the large swell expected). Danielle made its closest point of approach to our
east on the 28 August at a distance of more than 200nm. In the absence of wave recorders in
Bermuda, we can only estimate the wave heights – 24-hour forecasts for that day called for
significant waves and swells of up to 20 feet outside the reef.
RA IV/HC-XXXIII/Doc. 4.2(3), p. 2
1.3
Tropical Storm Fiona
Almost exactly the same scenario as for Colin played itself out during the approach and
dissipation of Tropical Storm Fiona, early in September. On Thursday 2 September, stable air
under a Saharan Dust Layer provided a hazy day. Even though the next day was expected to
remain similar, a Tropical Strom Warning was issued on Thursday night. Vertical wind shear
separated the low centre from the deep convection and reduced it to a tropical depression; it
was duly downgraded by the time it came within 100nm to the southeast of Bermuda. Early on
the 4 September, weakening TD Fiona brushed by to the east, bringing light to moderate winds
initially from the northeast, backing westerly then eventually southwesterly through the day, with
moderate to heavy showers & thunderstorms.
1.4
Tropical Storm Shary
Tropical Storm Shary was forecast to produce tropical storm force winds on the 29th and
30 of October, prompting a Tropical Storm Watch and later Warning. However, due its small
size, the interaction with a cold front to our west and its subsequent direction change away from
Bermuda, the local weather effects were minor. The center of Tropical Storm Shary passed 140
km (76 nm) southeast at 00UTC on the 30th of October, based on RADAR fixes.
th
2.
HURRICANE IGOR
All aspects of the storm’s approach, progress and departure went very well from the
perspective of BWS. The NHC track forecast was sufficiently accurate from an early stage that
we had adequate lead-time to prepare staffing levels, and even work out roughly when we
would be issuing watches and warnings. The intensity forecast was fortuitous, in that we were
able to justify the level of communications with the Emergency Measures Organization,
Department of Airport Operations, the Media and the public regarding the extent of preparation,
from an early stage. This in turn meant that most people took this storm seriously and took the
appropriate measures. Preparations made in anticipation of a hurricane, which was a full two
categories weaker than forecast when it actually hit us, meant that Bermuda was in a much
more ready stance than had the forecast been for a Category 1. If the forecast had been as
accurate in terms of intensity, would people & agencies have made the appropriate
preparations? This is difficult to ascertain until and unless we have a Cat 1 which is accurately
forecast as such.
Source www.nhc.noaa.gov - Infrared satellite image of Igor south of Bermuda on
Friday, 17 September, 2010
RA IV/HC-XXXIII/Doc. 4.2(3), p. 3
2.1
Staffing & Operations
We had the ideal level of staffing to be able to run the operation – some staff lived in St
David’s (the island on which BWS sits) and were able to go home Sunday night, returning
Monday morning via car. Others stayed the entire weekend. We would usually only have 2
people per 12-hour day and night shifts, but we actually had 4 forecasters and 3 observers on
hand, along with the Director (myself). We intentionally planned to have staff (including
management) prepositioned on the other side of the Causeway for continuity reasons, and to
ensure there was a ‘fresh’ crew to come in and relieve us all once the Causeway re-opened.
The staffing roster was adjusted to allow those who had been here all weekend to have a rest
period of at least 36 hours prior to their next shift.
Food and water was purchased early on, in anticipation of supporting the crew through
the weekend who might have had no scope to leave. Our training room was set up as a
sleeping area for those who were off shift, with cots, air mattresses, and blocked out windows
to the other lit areas of the office. The storm shutters were all down from an early stage also.
Vehicles were secured in the lee of the Air Traffic Control Tower and the alternate balloon
launch/generator building early on. Bikes were secured indoors.
Power, phones and internet never went down during the storm (we have a generator and
backups but never needed them), allowing us to continue to do our jobs unfettered by
technological limitations. Instruments which had not been safeguarded against the effects of
surge (most needed to stay in place for measurements e.g. wind towers, barometers) all
functioned remarkably well, with the exception of the GOES Satellite dish, which (as expected)
swung on its axis with the wind. Once the winds abated, our Ground Electronics Services
(GES) crew put it back into alignment. GES had a technician and the manager on hand 24/7 to
safeguard critical airport equipment and bring it back up once the storm had passed.
We launched 3 balloons during the storm itself, and only one was successful. This was
due primarily to the trees bordering the balloon launch deck at BWS, which ‘ate’ 1 balloon and 2
sondes. Only when the winds became a bit more southerly were we able to successfully
launch.
2.2
Storm Surge
Source: Bernews.com
RA IV/HC-XXXIII/Doc. 4.2(3), p. 4
This is a photograph from King’s Square in St. George’s, showing surge and wave action
above ground level. We must discover a means by which we can make accurate storm surge
predictions and observations. Currently there are no models on which to base accurate surge
predictions on a case by case basis, and the one verifying point (Esso Pier) is in a location
which is only helpful for the north side of St. George’s (where there are few properties near the
water). Data from that Tide gauge is outlined in the following graph, indicating a departure from
the predicted tide of approximately 1.75 ft at that site:
This may not be representative of the surge conditions in St. George’s Harbour (or indeed
in any other enclosed bodies of water around Bermuda), signifying a need to examine this
phenomenon more closely locally.
We did get some help from the NHC Storm surge unit, but the estimates provided are
vague and all-encompassing, instead of specific to each storm and location. This is not a
criticism of them (in fact they provided some guidance, when none was available from
elsewhere). However, we are not part of their modeling effort, as is outlined in this figure:
RA IV/HC-XXXIII/Doc. 4.2(3), p. 5
(Source: http://www.nhc.noaa.gov/ssurge/ssurge_slosh.shtml)
Things that would need to happen in order to get to a better level of storm surge
forecasting and observation:
1)
Accurate and high resolution bathymetry and coastal mapping – this is vital to the
effective modeling of surge. Without this, any accurate surge estimates that can be made will
be so broad-brushed as to not be useful.
2)
A real-time storm surge model which is configurable by storm, as opposed to a
generalized model. All storms have their own characteristics, so comparing Igor to Emily or
Florence would be inappropriate in term of surge, even though they all made direct impacts and
were Category 1 storms.
3)
Verification by way of measurement equipment – wave buoys and sea level gauges are
necessary to give us some data on which to verify the output, allowing us to tweak the model
appropriately.
RA IV/HC-XXXIII/Doc. 4.2(3), p. 6
2.3
Data & Impacts
POST STORM COUNTRY REPORT
Country: Bermuda
Tropical Cyclone: Hurricane Igor
Dates of data: 19-20 September 2010
Station
Bermuda
Airport TXKF
(10 min avg)
Fort Prospect1
St. David’s2
Commisioner’s
Point3
Maximum
Sustained
Wind
Maximum
Wind
Gust
Calm
Total
Rainfall
Direction
° True
150
Velocity
Knots
59
UTC
Date/Time
20/0223
Direction
° True
127
166
133
51.5
79
70
20/0350
20/0550
20/0340
166
166
133
Minimum
Sea
Level
Pressure
Velocity
Knots
81
UTC
Date/Time
20/0218
90
102
101
20/0530
20/0550
20/0340
mm
hPa
81
963.7
Automated wind and pressure measurements around the island during Igor, as outlined in the
chart above.
1 32° 17' 57.6882"N, 64° 45' 53.4774"W Elevation 230ft AMSL - 10-minute average
2 32°21.825’ N 64°39.368’W, Elevation 159ft AMSL - 10-minute average
3 32° 19' 44.5584"N, 64° 49' 55.9596"W Elevation 262ft AMSL - 10-minute average
RA IV/HC-XXXIII/Doc. 4.2(3), p. 7
Source: Hinson’s Island automated weather station (privately owned)
It was noted from some more high resolution (1 minute) sea level pressure data, Bermuda’s
pressure actually got down to 963.7 hPa at 2:51 UTC on the 20th (see below).
RA IV/HC-XXXIII/Doc. 4.2(3), p. 8
This is the barometer on which all of our official METAR/SPECI and SYNOP observations
are based. Also in the same screen shot are wind measurements from each end of the runway
at LF Wade International Airport. All of this data is from a Vaisala MIDASIV airfield integrated
weather observing system.
It was noted that the wind maximum associated with Igor didn't evenly bracket the
pressure trough as it would in a symmetric system. We have come to the conclusion that we
were probably experiencing some form of an extratropical Transition (ET) wind max at the
same time as the closest point of approach. This conclusion is largely based on the
satellite/radar signature, and Chris Fogarty's ET schematic, as shown below.
RA IV/HC-XXXIII/Doc. 4.2(3), p. 9
&
Meteosat IR Imagery for Igor’s passage near Bermuda at 0300UTC and Bermuda Radar
Sferics Lightning products from BWS for 2:56UTC.
Source: Dr. Chris Fogarty, Environment Canada Canadian Hurricane Center / Atlantic
Storm Prediction Center / National Lab for Marine and Coastal Meteorology
http://projects.novaweather.net/