Hurricane Nicole Post Storm Report Released

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NASA Terra/MODIS True Color satellite imagery of Hurricane Nicole near the time of closest point of approach 13 Oct 2016.

After each season, the National Hurricane Center prepares ‘post-storm reports’ on each tropical cyclone that formed in the North Atlantic and Eastern Pacific basins. These reports include data collected in real-time that may not have been available during operational analysis, and therefore can sometimes lead to revision of track or intensity. This was the case for 2014’s Hurricane Fay.

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Time trace of wind gusts (red ‘x’) and wind directions (green ‘triangles’) from the airport reproduced from the NHC report. We see the sharp decrease in wind gusts and sharp wind shift as the calm eye of Nicole crossed.

Today, the National Hurricane Center released its report on 2016’s Hurricane Nicole. Their analysis on observations from Bermuda suggest that widespread category one conditions occurred on the island with isolated areas seeing category two conditions. Aircraft reconnaissance measurements near the time of closest point of approach to Bermuda indicate that Nicole was still a category three hurricane with maximum sustained winds near 105 kts (120 mph). The island received impacts from the left-front quadrant of Nicole’s eyewall, missing these strongest winds (located in the right-front quadrant) and thus this was classified as a strike.

[strike, direct-hit, indirect-hitlandfall – Impact Terminology Defined]

Hurricanes are centers of extreme low pressure. Winds spiral inwards, towards centers of low pressure and in the northern hemisphere, this manifests as a counter-clockwise circulation.  Observations from Bermuda indicated that winds backed (turned counter-clockwise with time) from an easterly direction to a northerly, and then northwesterly direction suggesting that the center of circulation remained to east of the island and therefore did not make landfall, despite Bermuda entering the calm eye of the hurricane.

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Bermuda SRI Radar imagery showing steady and heavy rain rates persisting over Bermuda (red ‘+’) for hours before the drier eye and southwestern quadrant passed over the island. Reproduced from the NHC report.

Nicole’s impacts on Bermuda were also remarkable in that the hurricane made for one of the top-5 wettest meteorological days on record at the airport, and the Bermuda Weather Service was able to release a weather balloon in the eye that measured the highest precipitable water here since 1973 at 2.93″.

[What is Precipitable Water?]

Notable for an erratic early track and meteorological evolution (including two periods of rapid intensification), Hurricane Nicole will go down in the record books as the fourth early-October hurricane impact on Bermuda in three years. Once Nicole passed Bermuda, the cyclone underwent a complex transition into a powerful extratropical cyclone in the North Atlantic where it continued to produce storm force winds for several days.

Current Weather:

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Wind measurements at the Crescent, in the northern marine area via Bermuda Weather Service. Note peak in winds just before 9am 16 Feb 2017(sustained, to/gusts, middle).

Bermuda is now well into its ‘winter’ season where changeable weather associated with gales is commonplace. Yesterday’s cold front brought a brief warm and humid spell with southwesterly gales and thunderstorms that brought heavy rain to the island.

Locally severe wind gusts, mainly confined to the marine area, were also observed. The Crescent Buoy, in the northern marine area, measured a peak thunderstorm gust of 54 kts. Winds on island appear to have remained below severe levels (i.e. < 50 kts) with a peak gust of 43 kts measured at the airport prior to any thunderstorm activity.

Follow the Bermuda Weather Service for the latest official forecast, warnings, and observations for Bermuda.

Heavy Rains Summary

A well anticipated multi-day heavy rain event last weekend ended with a May’s worth of rain nearly everywhere. A band of deep, tropical moisture with total precipitable water amounts near 2 inches aligned over the island from Thursday night through Saturday afternoon. A cold front, turned stationary front remained draped nearby with associated small scale areas of low pressure developing along the front leading to isolated and brief periods of enhanced winds. The front and lows led to persistent shower and thunderstorm activity through much of the weekend resulting in some event disruption and nuisance flooding.

Officially, 3.82″ of rain was measured at the Bermuda Weather Service as a result of this rain storm. This agrees well with island-wide reports generally near 4 inches, including my PWS which measured 3.95″. In an average May, the island sees roughly 3 inches of rain.

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Distribution of rain across Bermuda showing a widespread heavy rain event. An islandwide average of 3.86″ fell. Each circle represents one observation. The shading is likely less reliable in areas of few observations. Observations from Bermuda Weather Service Facebook, Wunderground, and Davis WeatherLink.

Heavy Rain Event Looms

A blocked upper level flow pattern is currently developing. This will allow an upper trough to become stationary over the Eastern United States. Meanwhile, an associated cold front slides across the Western Atlantic today, becoming stationary near the island Thursday night. Convergent surface flow in an environment of deep layered moisture ahead of and along the stalling front will help to focus and maintain a region of shower and possibly thunderstorm activity near Bermuda.

High pressure remains in control Wednesday as it begins a retreat to the east. Pressure gradient between the high pressure to the east and advancing low pressure to the west lead to strengthening southerly winds on Thursday. Thursday night sees an initial band of showers ahead of the cold front. The cold front becomes roughly stationary nearby with waves of shower activity persisting through the day on Friday and into Saturday morning. The front then resumes its progression to the east, clearing shower activity as it exits the area.

Model guidance supports rainfall totals for the ~48 hour period Thursday night through Saturday morning of 2-4″. Depending on where the most persistent organized shower activity sets up, over 6″ of rain is possible in this period. Any persistent downpours contributing to these totals could lead to flooding, particularly around high tide and in low-lying areas.

Pay attention to the Bermuda Weather Service for the official forecast for Bermuda.

Heavy Rain and Strong Storms

March 29th saw a slow moving cold front push through Bermuda from northwest to southeast. Lines of thunderstorms associated with the front tracked across the island dropping very heavy rain in a short period leading to some morning flooding issues. Lightning strikes associated with those thunderstorms resulted in isolated electricity, and communications interruptions on Tuesday. Further still, one of the thunderstorms produced a waterspout off the west end of the island that was caught on film – a fairly rare occurrence with only 5 days per year seeing either a funnel cloud or waterspout/tornado from the airport for the period 2000-2015, mainly in August or September.

ConvectivePhenomena2000-2015
Using METAR/SPECI observations and monthly climate reports from the Bermuda Weather Service this summarizes the average number of each convective phenomena by month. Annually, one day per year sees hail, 39 days see thunder, and 5 days see a funnel cloud or waterspout/tornado. Data for the period 2000-2015 inclusive.

This heavy rain event followed a string of daily record high temperatures with temperatures in the mid-70s. Highs of 75.9ºF, 76.5ºF, and 76.5ºF broke records on the 26th (previously 75.8ºF set in 1999), 27th (previously 75.2ºF set in 1999) and 29th (previously 75.0ºF set in 1989) respectively. This warmth came with unseasonably high humidity as dew point temperatures held steady near 70ºF or oppressive levels through much of that period. This warmth and moisture likely played a role in fueling the thunderstorms observed on the 29th.

Experimenting with R-code and unofficial reports from Wunderground, I’ve put together this graphical depiction of the distribution of rainfall across the island. Apparently, the heaviest rains fell in the west end where over four inches of rain was reported in spots while parts of the east end saw less than an inch. Unfortunately, there are no rain reports on Wunderground from Hamilton or Sandy’s Parishes. Gaps in report coverage limits how accurately this map represents how much rain actually fell, so I’ve indicated where each report was made.

This heavy rain event follows another event with islandwide totals of over an inch of rain just two days earlier. The combination of these events has made March 2016 unusually wet, and has officially (at the airport) brought 2016’s year to date values roughly a month’s worth of rain above average.

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Distribution of rain across Bermuda shows higher storm totals to the southwest (unofficially more than four inches) and lower totals to the northeast where 0.92″ were officially measured at the Bermuda Weather Service (included in this plot.) The shaded areas are likely less reliable where there are fewer reports.

Mid-Week’s Heavy Rains

The 17th of February saw a very wet and active frontal system move across the island. With steady rain and embedded heavier showers and isolated thunderstorms. The widespread rains generally totaled more than two inches across the island, with the central parishes seeing the greatest totals. The 2.11″ of rain that fell at the Bermuda Weather Service was a daily record total for the 17th, beating the previous record of 1.76″ set in 1987. The wettest February day at the airport saw 3.80″ of rain on 21 February 1981.

This rain came on the heels of some of the coldest air of the season. The frontal system responsible for all this rain also ushered in a cold air mass in it’s wake with strong winds and below normal temperatures with lows around 55ºF on the 19th.

A quieter pattern is in store for the next five days with generally light to moderate winds and temperatures recovering to the low 70s, follow the Bermuda Weather Service for the latest official weather.

Below are Wunderground personal weather station reports for the meteorological day on the 17th. These are unofficial except where noted.

Location Rain Total
Devonshire, Devonshire 3.11″
South Road, Devonshire 2.77″
Chaingate Hill, Devonshire 2.67″
Wilderness, Smith’s 2.50″
McGall’s Bay, Smith’s 2.37″
Knapton Hill, Smith’s 2.36″
Tucker’s Town, St. George’s 2.20″
Bermuda Weather Service, St. George’s (official) 2.11″
St. David’s, St. George’s 1.78″
Cardinal, Southampton 1.77″
Hinson’s Island, Warwick 1.37″

Heavy Rains Tomorrow

EaUS 16 Feb 2016 2045UTC
GOES East RGB Satellite imagery showing cloud band associated with the approaching frontal system between the US East Coast and Bermuda.

A cold front and associated pre-frontal trough to the west of Bermuda is expected to reach the island early tomorrow with heavy rain, showers, and possible thunder.

Strong southerly flow ahead of the frontal system has allowed temperatures to climb into the low-70s and dew points to recover into the mid-60s after a cold and blustery weekend. Further warmth and moisture should continue to stream into place tonight. Showers with heavy rainfall rates are becoming increasingly likely, beginning early tomorrow morning. Over an inch of storm total rainfall is possible, mostly falling tomorrow. This could lead to some isolated flooding in low-lying areas, especially if this heavy rain occurs around the time of high tide.

Follow the Bermuda Weather Service for the latest official forecasts.

Active Winter Weather

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Infrared Satellite imagery around midnight Sunday into Monday showing significant winter low north of Bermuda. At this time, the low was moving northeastward and an associated cold front was passing Bermuda.

A series of non-tropical low pressure systems tracked across the Gulf of Mexico, across Florida and northeastwards past Bermuda bringing swings between warm and humid weather and cool and blustery weather separated by periods of rain and thunderstorms. The last of these lows passed Monday morning and has since merged into a massive low over the Labrador Sea.

This large scale low has been driving strong to gale force west-northwesterly winds across the Western Atlantic since Monday. A series of troughs embedded in that flow have each brought reinforcing cool weather, widespread showers, and renewed winds to the island. This has led to some of the coldest weather for Bermuda so far this season with a low temperature last night in the mid-50s. A further trough embedded in this persistent flow is expected to bring a final reinforcement of cool weather to Bermuda on Thursday afternoon/evening and a Gale Warning is in effect for winds possibly reaching gale force over exposed and elevated areas as that system passes.

High temperatures are typically near 69ºF while lows are typically near 61ºF this time of year. Yesterday and today are some of a handful of below normal temperatures so far this winter.

A transient ridge of high pressure calms winds on Friday. Winds then reverse, coming out of the east Friday night and increasing as the ridge moves away to the north and northeast. A powerful coastal storm developing in the Mid-Atlantic region of the United States then draws a warm front northwards across Bermuda on Saturday morning allowing wet but warmer weather on Saturday before its respective cold front passes Saturday night with renewed cool weather. Strong easterly winds veer to the south on Saturday behind the warm front. Southerly winds slowly veer to the southwest through Saturday and increase to near gale force. The cold front passes Saturday night and southwesterly winds remain near gale force and slowly veer to the west on Sunday.

Follow the Bermuda Weather Service for the latest official forecast and warnings.