WORLD METEOROLOGICAL ORGANIZATION
RA IV/HC-36/Doc. 4.2(1)
(03.III.2014)
___________________________________________
RA IV HURRICANE COMMITTEE
THIRTY-SIXTH SESSION
ITEM 4.2
CANCUN, MEXICO
ENGLISH ONLY
7 TO 10 APRIL 2014
REVIEW OF THE PAST HURRICANE SEASON
Reports of hurricanes, tropical storms, tropical disturbances and
related flooding during 2013
Report from Bermuda
(Submitted by Bermuda)
RA IV/HC-36/Doc. 4.2 (1), p.2
Table of Contents
Review of 2013 Season ................................................................................................................... 2
Tropical Storm Gabrielle, September 10th – 12th.............................................................................. 2
Summary Table - 2013 Tropical systems that affected Bermuda .................................................... 8
REVIEW OF 2013 SEASON
Bermuda experienced a significantly less active tropical cyclone season than during
2012, as was typical across the whole Atlantic basin.
Only one tropical cyclone, Tropical Storm Gabrielle, had any significant impact, although it is
worth noting that this storm was essentially a direct hit and warranted a Tropical Storm
Warning.
Distant Hurricane Humberto provided long period swells, bringing enhanced surf
conditions on the South Shore, whilst although Tropical Storm Melissa provided shorter
period swells, its relatively proximity to Bermuda (500 nm closer than Humberto) generated
more significant easterly swells, warranting a Small Craft Warning (for seas 9 ft or more).
TROPICAL STORM GABRIELLE, SEPTEMBER 10TH – 12TH
TD7 was identified by aircraft reconnaissance just south of Puerto Rico, at 1800 hrs
(local Bermuda time) on Wednesday 4th September 2013, and it intensified to Tropical Storm
Gabrielle as it approached western Puerto Rico and eastern Hispaniola. TS Gabrielle then
dissipated into a remnant low (0000 hrs Friday 6th September) as it moved over the eastern
fringes of the Dominican Republic.
RA IV/HC-36/Doc. 4.2 (1), p.3
On Friday 6th September, Bermuda Weather Service (BWS) advised the local
Emergency Measures Organisation (EMO) to keep a watch on the remnant low of Gabrielle
as redevelopment was possible on Bermuda’s doorstep early the following week. This was
an important step as communication and media/news outlets are typically at a minimum over
the weekend.
A well sheared environment prevented any further development of the remnant low
as it moved north-northeast over the weekend and into Monday 9th September. However,
later that night deep convection developed and persisted, especially around the eastern side
of the circulation. An Ascat overpass confirmed winds up to tropical storm force and as
such, advisories were reinstated at 0600 hrs (local Bermuda time) on Tuesday 10th
September for the redevelopment of TS Gabrielle.
The short term forecast for TS Gabrielle put the storm on a heading north towards the
western fringes of Bermuda’s marine area, with a closest point of approach within 25
nautical miles of the Island (inside our marine area) at around midnight on the Tuesday.
After consultation with NHC at 0300 hrs, BWS agreed to issue a TS Warning in concert with
the 0600 hrs NHC advisory. In accordance with this agreement, Bermuda Weather Service
issued a Tropical Storm Warning as of the regular early morning forecast update at 0530
hrs.
The official BWS forecast, adjusted slightly during the course of the 10th September
(with further updates from NHC and the associated Hurrevac data), called for increasing
winds (45-55 knots for a time overnight with gusts to 70-75 knots, especially in exposure and
across elevated parts of the Island) with developing showers and rain, as well as the risk of
embedded thunder. Seas were forecast to rise to as high as 18 feet outside the reef.
Although not specifically mentioned in the official BWS forecast products, a storm
surge of up to 2-3 feet was estimated by NHC, with rainfall amounts of 3-5 inches, locally 7
inches. Rainfall amounts were tapered back a bit during further conference calls with NHC,
partly because a lot of the deep convection was being sheared to the east of Bermuda.
As forecast, winds gradually increased to tropical storm force by early evening, and
isolated showers in the day increased to more persistent rain later in the evening. TS
Gabrielle made passage to our near west (approx. 22 nm to the west of the city of Hamilton)
around 0100 hrs on Wednesday 11th and this was also well forecast. As it began to slowly
move away northwest, conditions gradually improved during the morning of the 11th, and the
Tropical Storm Warning was dropped at 0900 hrs, with a Small Craft Warning taking its
place for strong winds (20 knots or more) and locally rough seas outside the reef (9 feet or
more).
Rainfall for the main duration of the event, from the early morning of the 10th through
the early afternoon of the 12th (06z on 10th to 18z on 12th), amounted to 1.43 inches at
Bermuda Weather Service, although greater amounts are likely to have fallen across other
parts of the Island according to informal reports and radar imagery. As intimated earlier, the
NHC rainfall estimates, as per the Hydrometeorological Prediction Center, were initially
overforecast, and part of the reasoning for this appeared to be the fact that more of the deep
convection associated with TS Gabrielle was sheared to the east (offshore of Bermuda) than
forecast by the computer models.
RA IV/HC-36/Doc. 4.2 (1), p.4
Main impacts of Tropical Storm Gabrielle on Bermuda were the strong winds which
downed tree branches, palm fronds and other foliage, some minor infrastructure damage
(report of a dock and boat damaged in Dockyard), and a minimal storm surge (estimated to
have been around 1 foot by a BWS forecaster on the south side of St George’s – note that
the NOAA Esso Pier buoy located on the north side of St George’s actually recorded slightly
below average tides during the event, possibly due to lee effects). Minor power outages
were recorded across the Island. August was a very wet month with over 10 inches or rain
(approximately twice the average), and as such much of the flora was overgrown, likely
contributing to enhanced foliage damage.
A few flights at L. F. Wade International Airport and some commuter/tourist ferries
were cancelled. In addition, the Norwegian Dawn, a regular cruise ship visitor in port at
Dockyard, was tied up with extra precaution. The Government decision to close all public
schools for the 11th was overturned in the early morning of that day after assessment of the
road network and power to schools. As it transpired, only a few remained closed due to
power outages.
As has been the case with other recent tropical storms, one of the biggest challenges
for BWS has been pressure to communicate exact details of strength and duration with
confidence, especially of the 50 knot sustained wind threshold, which significant operational
decisions are based on. However, due to the size of Bermuda, any slight changes in tropical
storm track and intensity can have significant impacts for the Island, and consequently a
widely varying forecast. BWS always strive to convey the level of uncertainty of a particular
tropical cyclone with the forecast, but this is sometimes of limited use to higher level decision
makers who have to make a judgement call.
BWS continue to enhance their communication with higher level decision makers, in
order to mitigate the issues above as much as possible. In addition, as of the 2013
Hurricane Season, a text message notification system to the public via the two main cell
phone providers, Digicel and Cellone, was established. Shortly after the initiation of the
Tropical Storm Warning, this new communication method was executed, with all
Digicel/Cellone subscribers being sent a message similar to that below on their cell phones:
EMO Alert: Tropical Storm Warning has been issued at 6am for Bermuda for
TS Gabrielle. Monitor www.weather.bm for the detailed forecast.-EMO
There was some delay in receipt by some subscribers. This was due to local network
limitations of disseminating a timely message to tens of thousands of subscribers.
A video of the Post TS Gabrielle briefing by the Minister of Public Safety, the Hon.
Michael Dunkley, is available at: http://www.youtube.com/watch?v=IEl26716QNA
Table of maximum winds (sustained and gusts) at various locations across Bermuda
(ranging from near sea level Airport/Causeway to approx. 290 ft at Harbour Radio), generally
around evening time:
RA IV/HC-36/Doc. 4.2 (1), p.5
Location
Maximum sustained wind
Maximum gust
LF Wade International
Airport
39 knots
49 knots
Commissioner’s Point,
Dockyard
47.5 knots
58.9 knots
Causeway sensor
38 knots
55.3 knots
Harbour Radio
50 knots
65 knots
Verification – referencing the table above, the forecast for a period of sustained winds of 45
knots with gusts to 55 knots during the evening was well verified. Gusts were only a little
below forecast with Harbour Radio recording 65 knots, compared with the forecast of 70-75
knots. However, overnight the winds did tend to die down quicker than forecast.
Nevertheless, the Tropical Storm Warning verified and was wholly appropriate for the
conditions experienced across Bermuda and the local waters.
Ascat satellite overpass (2200 hrs local time on the 10th) clearly showing the
circulation of TS Gabrielle just south of Bermuda:
RA IV/HC-36/Doc. 4.2 (1), p.6
In addition, satellite and radar images are provided below:
Satellite image for 2015 UTC on 10th September:
RA IV/HC-36/Doc. 4.2 (1), p.7
Radar image for same evening at approximately 2200 hrs local Bermuda time:
NOAA tide data for Esso Pier:
RA IV/HC-36/Doc. 4.2 (1), p.8
SUMMARY TABLE - 2013 TROPICAL SYSTEMS THAT AFFECTED
BERMUDA
Summary Table
Storm Name
TS Gabrielle
TS/HURCN
Humberto
(distant east)
STS/TS Melissa
(distant east)
Month
Watch/Warning
Issued for
Bermuda
Maximum Wind
Speed at LF
Wade
September 10-12th Tropical Storm
Warning issued
0530 hrs 10th,
ended 0900 hrs
11th
September 16-17th *N/A
39 knots gust 49
knots around 1930
hrs on 10th
November 18-20th
N/A
Small craft
warning issued at
1130 hrs 18th due
to easterly swells
*N/A
*Although Humberto did not produce wind/seas significant enough to warrant any warnings, it did
produce enhanced long-wave swells along the South Shore