Two Weekends, Two Damaging Storms

Gonzalo Fay Tracks
Tracks of Tropical Storm Fay (white, right) and Hurricane Gonzalo (red, left) earlier this month. Tracks derived from National Hurricane Center Advisories plotted in Google Earth.

Tropical Storm Fay

Tropical Storm Fay struck Bermuda with violent northwesterly winds around dawn on Sunday, October 12th. The tropical storm had maximum 1-minute sustained winds near 70mph when it passed very near or over the east end of the island. Winds on Fay’s approach were near tropical storm force and easterly, and were followed by a brief calm as the center made its closest approach to the island. This respite was short lived and was concluded with a wind shift to the northwest leading to a rapid increase in winds to damaging near hurricane force with gusts exceeding that, especially in elevated areas exposed to winds from the northwest.

Here are a list of various preliminary peak sustained wind and gust reports from Fay. The Bermuda Weather Service AWOS, Airport, NDBC Bermuda Esso Pier Site, and my Personal Weather Station.
Here is a map of various preliminary peak sustained wind and gust reports from Fay. The Bermuda Weather Service AWOS, Airport (Official), NDBC Bermuda Esso Pier Site, and my Personal Weather Station. NOTE: The sustained winds use varying averaging periods from 1-minute to 10-minutes, further, they are all at different elevations and exposures – these factors have an impact on both sustained winds and gusts. Further, being preliminary, these figures are subject to change.

A Tropical Storm Watch was issued for Bermuda as soon as Sub-tropical depression 7, later named TS Fay, formed about 590miles south of Bermuda. This was because it was forecast to strengthen into a Sub-tropical Storm and pass near to the east of Bermuda on Sunday Morning. A Tropical Storm Watch is issued when tropical storm conditions (1-minute sustained winds between 39 and 73mph associated with a tropical or sub-tropical cyclone) are possible in Bermuda or the surrounding marine area within the next 48hours. Since the depression formed Friday morning, and was expected to pass to the near east of Bermuda on Sunday morning, watches were appropriate here.

NHC TWO October 8th 2pm
National Hurricane Center 5-Day tropical weather outlook first mentioning the chance for development of what became Hurricane Fay. At this time (4 days before striking Bermuda) they gave the disturbance a 20% chance of becoming a Tropical Cyclone in the next 5 days.

However, late on Friday night, with the midnight local time advisory from the National Hurricane Center (12 hours later), and the onset of tropical storm conditions therefore at least possible within the next 36hours in the marine area, it is arguable that the issuance of tropical storm warnings would have been appropriate here. By this time, Fay had evolved into a lopsided storm with unusual structure – most of its deep convection and strongest surface winds were found to the left of the center. With the center expected to pass to the right (east) of Bermuda, that would not only put Bermuda in Fay’s region of tropical storm force winds, but close to or in Fay’s worst conditions. A Tropical Storm Warning is typically issued when tropical storm conditions are expected in Bermuda or the surrounding marine area within the next 36hours. A tropical storm warning was issued with the 6am local time advisory on Saturday morning, giving between 12 and 24hours of lead time before tropical storm conditions were expected to develop in the marine area.

In addition to the Tropical Storm Warning, a Hurricane Watch was issued with the 6pm local time advisory from the National Hurricane Center as Hurricane conditions (1-minute sustained winds greater than 74mph associated with a tropical or sub-tropical cyclone) became possible in Bermuda or the marine area within the next 12hours in this case (typically issued for such conditions possible within the next 48hours).

[Learn more about Watch and Warning Criteria in the BWS Glossary]

Annotated Fay Radar
Bands of deep convection seen on Bermuda Weather Service Radar rotating around the center of Fay from northwest to south across Bermuda. Note that most of the deep convection is to the northwest and west of the center estimated with a red ‘x’. This radar image was at 7:13am local time, October 12th 2014.

It was confidently forecast from the beginning that Fay could bring tropical storm conditions to Bermuda, yet there was arguably a delay in issuing Tropical Storm Warnings of 6-12hours. Conversely, it was very unlikely that hurricane conditions would occur until Fay became a stronger storm and it became apparent that the core of deepest convection and strongest winds would pass near or over the island. So there was a confusing delay in issuing the Tropical Storm Warning, but an appropriate delay in issuing a Hurricane Watch. Given the information available at the time, a Hurricane Warning would not have been appropriate.

Regardless of watch/warning semantics, Fay was discussed in some form or another in both the public and marine forecasts from the Bermuda Weather Service even as a precursor disturbance more than five days in advance. Therefore, the public should have been at the very least adequately aware of inclement weather expected for the weekend – potentially associated with a tropical cyclone for the entire week leading up to the event. The peak gusts from Fay appear to be somewhat unexpected with widespread gusts well over 100mph at exposed elevation. The National Hurricane Center advisory before Fay’s closest approach indicated gusts near 75kts or 86mph were possible with higher winds at elevation and exposure.

It is important to remember that the inner core structure of each individual tropical cyclone can be vastly different and where Bermuda is in relation to that inner core can so it is often inaccurate to compare the impact of individual storms as a result. Each storm should be taken seriously and proper preparations should be made. This led to damages from not properly storing outdoor items, not securing boats, and not boarding up windows etc. That being said, much of the additional tree and structural damages that resulted from Fay would have been hard to avoid regardless of preparation. The Royal Gazette reports that BF&M has dealt with insured damages from Fay near $3.8million so far.

Hurricane Gonzalo

Following closely on Fay’s heels, Hurricane Gonzalo delivered the second blow to the island the following weekend. The night of Friday, October 17th saw the landfall of Hurricane Gonzalo on Bermuda as a category two hurricane with 110mph 1-minute sustained winds. With Gonzalo forecast to hit the island so soon after Fay’s largely unexpected ferocity, residents apparently took preparations much more seriously for Gonzalo.

Hurricane Gonzalo Prelim Wind reports
Here is a map of various preliminary peak sustained wind and gust reports from Gonzalo. The Bermuda Weather Service AWOS, Airport (Official), NDBC Bermuda Esso Pier Site, and my Personal Weather Station. NOTE: The sustained winds use varying averaging periods from 1-minute to 10-minutes, further, they are all at different elevations and exposures – these factors have an impact on both sustained winds and gusts. Further, being preliminary, these figures are subject to change.

Gonzalo was completing an eye wall replacement cycle and simultaneously beginning a drawn-out transition to a post-tropical cyclone as it crossed Bermuda. Unique cyclone structural elements developed in the core of Gonzalo as a result and lashed the island with hurricane conditions from the east-southeast and east, then, following a relatively brief calmer period, from the west-northwest and west.

At midnight local time on October 14th-15th, the Bermuda Weather Service issued a Hurricane Watch for Bermuda. While this typically means that Hurricane conditions are possible in Bermuda or the surrounding marine area within the next 48hours, in this case it meant that the onset of tropical storm conditions was expected in those areas in the next 48 hours and those conditions would make preparation for the possible hurricane conditions dangerous. In effect this gave Bermuda 60 hours of advisory lead time before the onset of tropical storm conditions. This was made possible by very confident forecast track likely enhanced by invaluable aircraft collected observations in Gonzalo. Watches were upgraded to warnings on Wednesday (October 15th) afternoon as confidence in storm track increased and Gonzalo continued its approach.

On Gonzalo’s final approach to Bermuda, the inner eye wall began to collapse and an outer eye wall wrapped around the southern side of the storm and began to take over. As this happened, Gonzalo weakened from a category four hurricane with 130mph 1-minute sustained winds to a category three hurricane with 115mph 1-minute sustained winds.

[Learn more: Saffir-Simpson Hurricane Wind Scale]

Hurricane Gonzalo Radar EWRC Analysis
Long Range Bermuda Weather Service Radar imagery showing the changing structure of Hurricane Gonzalo as the storm approached. You can see how the inner eye wall structure falls apart as the outer eye wall structure builds. Keep in mind that as Gonzalo was approaching it was also coming into radar range and that has an effect on the intensity of radar returns. Click for larger image.

Gonzalo’s outer structure consisted of a main rain shield of light to moderate rain associated with the central dense overcast, and one spiral band with convective cells of heavy rain embedded within that main rain shield. Some of these convective cells exhibited hook echo features in radar reflectivity, but had little rotation when looking at radar velocity. There is therefore little evidence to suggest that there was any tornadic activity here. This spiral rain band resulted in locally gustier winds; further, by the time it was impacting Bermuda, the island was already experiencing tropical storm conditions with winds out of the east-southeast.

As Gonzalo continued to approach, hurricane conditions were occurring in elevated areas exposed to east and east-southeasterly winds by 6pm as the northern eye wall of Gonzalo began to move over Bermuda. The northern eye wall consisted of the new outer eye wall with a convective burst forced by convergence left by the remnants of the old inner eye wall from the eye wall replacement cycle that was partly responsible for Gonzalo’s weakening on approach. This convective burst passed over the island and its vigorous upward motions allowed for very high rainfall rates to accompany hurricane conditions.

CommisionersPt and StDavids Meteogram_Annotated
These are meteograms for Commissioner’s Point (Dockyard) on top, and St. David’s Lighthouse on bottom. In each plot the top red line is wind gust, the bottom red line is sustained wind, the green line is wind direction, the yellow line is temperature, and the purple line is relative humidity. Some wind directions are marked in green words (eg. “East”), and the 64kts (hurricane force wind) line is estimated in white. Most recent observations are to the right.

The now large eye of Gonzalo (thanks to the eye wall replacement cycle) began to move over the island by 9pm local time. Winds quickly dropped off from hurricane force and became light. Light winds now at Dockyard backed sharply east to north to west, while winds at the airport and St. David’s veered sharply east to south to west during the more than an hour of light winds in the eye. This pattern of wind shifts as observed on each end of the island is consistent with the center of a low pressure (ie. a Hurricane) passing between the two locations. Further, during this time, sea level pressure bottomed out near 953mb at the airport and around the island. These observations indicated that Gonzalo had indeed made landfall on Bermuda, these Bermuda Weather Service AWOS observations reveal the classic signature of landfall.

As the light winds of the eye began to move away, the island entered the southwest and southern eye wall of Gonzalo. Heavy rains moved in with renewed hurricane force winds from a west and west-northwest direction. The difference between gusts and sustained winds was larger in this region as compared to the northern eye wall and that may have had an impact on the damage pattern for this wind direction. The wind traces at both Commissioner’s Point and St. David’s Lighthouse also indicated two wind maxima in the southern eye wall one around midnight and another around 1am local time.

As the southern eye wall pulled away from the island, ending hurricane conditions after 1:30am local time, isolated to scattered showers moved in and continued to produce hurricane force gusts for another two hours in elevated and exposed locations before winds subsided at a much quicker pace.

Bermuda Storm Surge
Preliminary water level data from the NDBC site at Esso Pier on the north side of St. George’s island.

While Gonzalo had a similar strength and intensity to Fabian, the track of Gonzalo (over Bermuda, rather than west of Bermuda) kept Gonzalo’s strongest winds to the east of the island, and winds largely paralleled the island. This meant that there were fewer places for storm surge to build up and become dangerous and damaging. Coastal flooding was therefore less of an issue with Gonzalo compared to Fabian as a result. A tide sensor on the north side of St. George’s island measured a peak storm surge during low tide during the southern eye wall, this had the effect of the tide not receding from the previous high tide at that location. Assuming a similar magnitude of storm surge during the northern eye wall in areas where easterly winds are onshore – Gonzalo might have resulted in a storm tide of near 5feet which would have resulted in minor coastal flooding of 1-2feet in east facing coastline.

Gonzalo’s winds added to the structural damage to buildings and vegetation from Fay and resulted in an island wide blackout affecting around 85% of BELCO’s customers. The Royal Gazette reports that damage from Gonzalo will likely be $50-100million.

Fortunately, there were no reported fatalities in either storm. A testament both to Bermuda’s well tested emergency management procedure and building codes designed for such adverse weather.

Lessons learned from Fay and Gonzalo: It is possible that much of the public were in a mindset of ‘its only a tropical storm’ therefore I don’t need to seriously prepare before Fay struck the island. It is important to remember that, Bermuda has been fortunate to not have experienced winds of the magnitude of Fay since Hurricane Igor in 2010. Similarly, Gonzalo brought winds not experienced on Bermuda since Hurricane Fabian in 2003. If anything, these back-to-back tropical cyclones demonstrate that communication of warning and advisory products in meteorology remains something that needs be improved. For Fay and Gonzalo the same terminology ‘Hurricane Watch’ meant very different things. This is another example where meteorologists worldwide are struggling to balance following warning criteria with the forecast impacts to society. The challenge being – communicating the impacts effectively.

[catch up on Hurricane Igor’s impact on Bermuda from this NHC Tropical Cyclone Report]

As always it is important to follow official updates from the Bermuda Weather Service (the only official source of weather information for Bermuda) to stay aware of and prepared for any inclement weather. Updates from any other source are unofficial for Bermuda and might not take into account local and regional effects. Often these forecasts are extracted directly from computer models that cannot resolve the island. Further, if they are reviewed and subsequently adjusted by a human, that person often has little experience with Bermuda.


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