Torrential January Rains

Observations around Bermuda indicate a widespread 4-6″ of rain fell with isolated areas seeing >6″. Reports are sourced from Wunderground, WeatherLink, and Bermuda Weather Service.**Note that shaded areas on this map with fewer reports are less reliable.**

A deep long-wave upper level trough over the Eastern United States slowly edged eastwards on Thursday morning, this allowed a cold front to slowly advance towards and across Bermuda. Deep-layered flow out of the tropics allowed significant moisture transport across Bermuda. The frontal system, supported by upper level dynamics, was able to make use of that moisture in the form of an active band of heavy showers and thunderstorms that slowly progressed across the island, with a trailing region of light-moderate rains.

Rain totals for the meteorological day (0600 UTC to 0600 UTC) at the Bermuda Weather Service far exceeded several records, with 5.34″ of rain. This led to widespread flooding of low-lying and poor-drainage areas (see: Royal Gazette, Bernews). Furthermore, this rain total is roughly the amount of rain that Bermuda typically gets for the entire month of January. The 1981-2010 average January rainfall is 5.43″, or 5.30″ for 1971-2000 climate period.

Table: Records broken with yesterday’s rain, with reference to single, meteorological day records for the period 1949-present at Bermuda Weather Service.
Type of Record Previous Record
Record Wettest for the date 5 Jan 1.54″ (5 Jan 1994)
Record Wettest Jan Day 3.99″ (11 Jan 1986)
Record Wettest Winter (Dec-Jan-Feb) Day 3.99″ (11 Jan 1986)
5th Wettest Day (1.) 7.77″ (1 Jun 1996)
(2.) 6.77″ (13 Oct 2016 – Hurricane Nicole)
(3.) 6.21″ (31 Aug 1982)
(4.) 5.52″ (14 Jul 1980)
(5.) 5.34″ (5 Jan 2017)
(6.) 5.24″ (29 Oct 1967)

It is particularly impressive that this event made it into the top-5 wettest meteorological days because it occurred in winter. Rain events in winter typically produce lower totals for two main reasons, compared to summer events:

  1. these are typically associated with frontal systems that generally pass quickly
  2. there’s typically not as much atmospheric moisture available in winter

This event was associated with a frontal system, but it was progressing very slowly, and there was unusually high amount of atmospheric moisture available for rain because of the deep-layered flow from the tropics ahead of the system.

Model guidance performed well at picking up on the potential for a heavy rain event on the 5th since the end of December. This was reflected in the Bermuda Weather Service forecasts and forecaster’s discussion several days before the event.

More heavy rain is in the forecast

Yesterday’s front has progressed to the East of Bermuda, clearing its rainy weather with it. This is allowing much drier weather to settle in. However, an area of low pressure and frontal system, organizing over the lower Mississippi Valley today, will result in a similar frontal set-up to yesterday’s system over Bermuda at the end of the weekend.

Over the weekend, the low will push off the US East coast and track northeastwards around a long-wave trough over Eastern North America. As it does this, deep-layered southerly flow out of the tropics resumes ahead of a trailing cold front. This front will slowly progress eastwards toward Bermuda, passing on Sunday.

Model guidance is once again suggesting potential for a heavy rain event associated with this system. This is mentioned in the Bermuda Weather Service forecast and forecaster’s discussion. With soil freshly saturated, additional flooding in low-lying and poor-drainage areas is possible on Sunday.

A significant cool-down is then expected to start the work week. Temperatures are likely to struggle to reach 60°F on Monday as a continental polar airmass is drawn off of North America from the northwest across Bermuda.

See the Bermuda Weather Service for the latest official forecasts, warnings, and observations for Bermuda.

Tudor Hill Observatory

Tudor Hill Marine Atmospheric Observatory (Credit: BIOS)

In a project commissioned by the National Oceanic and Atmospheric Administration’s (NOAA) Earth Systems Research Laboratory (ESRL) the Bermuda Institute of Ocean Sciences (BIOS) has been the cooperating agency responsible for measuring the concentration of key atmospheric atmospheric gas species at Tudor Hill in Bermuda. This is part of NOAA/ESRL’s Global Monitoring Division’s aim to track changes in these key gas species, particularly focusing on their sources, sinks, global trends, and distributions.

[About: Global Monitoring Division]

One of the more well known gases measured at these types of observatories, including Tudor Hill, is Carbon Dioxide. An infamous greenhouse gas emitted largely through the burning of organic matter (ie. fossil fuels), the increase in Carbon Dioxide can be seen even in the middle of the Atlantic at Tudor Hill, Bermuda.

Another interesting feature is the seasonal change in Carbon Dioxide concentration controlled mainly by the biosphere. Because there is more land in the northern hemisphere, the biosphere’s influence is disproportionally weighted to what is happening in the northern hemisphere. During northern hemisphere summer, there are more photosynthetically active plants taking in more Carbon Dioxide globally than during northern hemisphere winter.

Measurements of concentration of Carbon Dioxide gas at Tudor Hill Bermuda since records began in 1989, including preliminary 2016 data in orange. Plotted with NOAA/ESRL’s interactive data viewer.

Attributing the trend in Carbon Dioxide to human activity is a little more complicated than just observing the trend. It comes through analysis of Carbon isotopes bonded in Carbon Dioxide. Carbon comes in two naturally occurring stable isotopes: Carbon-13 (13C) and Carbon-12 (12C). 13C has an additional neutron and therefore has slightly more mass and slightly different chemical properties.

It has been found that the biosphere (ie. plants) preferentially uptake the lighter 12C containing molecules during photosynthesis. This leaves behind less 12C in the atmosphere and so the ratio 13C/12C increases. The higher proportion of 12C in organisms is maintained even if they should become fossil fuels. When we burn organic matter (ie. fossil fuels) we release Carbon Dioxide with higher proportions of 12C into the atmosphere and the ratio 13C/12C measured in the air decreases as a result.

One way to measure the relative amount of the two stable Carbon isotopes is called “delta 13 Carbon” (δ13C). Here, the measured ratio 13C/12C is standardized by a reference ratio determined from reference research into the average properties of Carbon. That standardization is very close to one, and all the variations occur in the thousandths decimal. In practice, one is subtracted from it and then the result is multiplied by 1000.

A trend of decreasing δ13C is observed at Tudor Hill, Bermuda. This trend lends support to the idea that not only are atmospheric Carbon Dioxide concentrations increasing, but the increase might be due to human activity.

All available delta thirteen C data for Tudor Hill, Bermuda. Records of this parameter are kept since 1991, including preliminary 2016 data points. Plotted with NOAA/ESRL’s interactive data viewer.

These trends and patterns are repeated across the world. It is clear that the upswing in Carbon Dioxide is not a local phenomenon, but a symptom of a global problem.

Many more projects, providing invaluable scientific insight rely on data like this collected at Tudor Hill in Bermuda and around the world. Bermuda has proved to offer a unique location to get continuous long time-series of the largely undisturbed samples of the low-level ambient marine atmosphere. As such, I expect research to continue or expand in Bermuda, particularly as issues such as increasing Carbon Dioxide concentrations become more pressing.

Carbon Isotopes in Photosynthesis (Marion H. O’Leary, 1988)
NOAA/ESRL’s Global Monitoring Division
->Map of Observation Sites
->Tudor Hill’s Measurements via Interactive Data Viewer

Nicole’s Direct Hit

Hurricane Nicole passed very close to Bermuda midday on Thursday 13 October as a strong category three hurricane. Preliminary center fixes indicate that Nicole passed about 9 nm (10 mi) east of Bermuda at noon on Thursday with maximum sustained winds near 105 kts (120 mph). At this time, Nicole’s eye was about 30 nm (35 mi) wide, and so Bermuda briefly entered the calm of the eye, but not before enduring hours of violent winds and torrential rain that led to isolated structural damage, significant utilities disruptions, and widespread flooding in coastal areas, low-lying areas, and poor-drainage areas.

Visible satellite image of Nicole near time of closest approach. At this time, the entire island was experiencing the relative calm of the eye. An approximate track of Hurricane Hunter flight through Nicole is overlaid in red, starting at A in the bottom right.

After peaking as an extremely dangerous category four hurricane the night before impacts on Bermuda were felt, Nicole began to weaken on its final approach on the island. Vertical wind shear had markedly increased during this time, disrupting the circulation and degrading the convective organization. The solid ring of deep convection around the eye, aka the eyewall, opened up into a semi-circle that became more poorly defined as the hurricane approached.

[See these changes on long radar loops of Nicole’s approach Here]

Traditional hurricane structure and observations from ongoing Hurricane Hunter missions suggest that the strongest winds of Hurricane Nicole missed Bermuda to the east as the island saw effects from the northern and then western parts of the eyewall, not the eastern eyewall where, in this case, the strongest winds would have been found. However, damaging hurricane force winds were observed for several hours, mainly as the northern eye wall of the hurricane crossed the island.

Peak gusts in this part of the hurricane were measured up to 118 kts (136 mph) at an unofficial station at Commissioner’s Point, while the official peak winds measured at the airport reached gusts of 91 kts (105 mph). The peak official 10-minute sustained winds reached 68 kts (78 mph) at the airport. Areas exposed to easterly winds, particularly near hill tops, likely saw the highest winds in Nicole.

Additionally, the Bermuda Weather Service was able to get an estimate of rainfall total at their office. During the hurricane, 6.77″ of rain was caught. This makes 13 October 2016, the wettest October day on record, beating the previous record of 5.24″ set on 29 October 1967. This rain comes on the heels of a very wet week prior to the hurricane and a record wet September as 11.80″ of rain was observed for the month, beating the previous record of 11.15″ in September 1983.

An official and comprehensive post-storm summary will be released by the National Hurricane Center in the coming months.

Nicole Set for Direct Hit Tomorrow Morning

Follow the latest official updates from the Bermuda Weather Service and the National Hurricane Center. Below are my unofficial thoughts.

The core of now category two Hurricane Nicole is expected to pass near or over Bermuda early on Thursday. As of the 3pm advisory from the NHC, this could mean dangerous coastal flooding from a 6-8 foot storm surge, flooding away from the coast due to heavy rain of 4-8″, and isolated damage from possible tornadoes. Tropical storm conditions are expected to begin after midnight tonight and last through much of Thursday with a period of hurricane force winds beginning Thursday morning lasting through mid-afternoon. Sustained winds are expected to peak near 90 kts (105 mph), and will be higher in elevated and exposed locations (possibly near category three strength) with higher gusts.

Hurricane Nicole just after 12pm advisory on RGB GOES multispectral satellite imagery, Bermuda can be seen at the top of this image to the north-northeast of Nicole.

Last night, Nicole quickly strengthened from a tropical storm to a category two hurricane, increasing winds by 30 kts and decreasing pressure by 21 mb in the 24 hours between 12pm yesterday and today. Nicole had stalled or drifted slowly to the west during this time as it interacted with the front left behind as the extratropical remnants of Matthew exited the Canadian Maritimes and left Nicole in a weak steering environment.

Nicole is poised for some additional modest strengthening as the hurricane sits in a region of warm sea surface temperatures (~28 °C), low vertical wind shear, and generally high moisture content. However, some drier and more stable air to the west, might be intermittently wrapping into the circulation and slowing the pace of intensification. Nicole is expected to be a strong hurricane and it is still possible for Nicole to become a major hurricane before reaching the island.

The track forecast philosophy has proved true for the last five days and hasn’t changed; Nicole has made the turn to the north and is still expected to pass close to or over Bermuda Thursday morning as it turns more northeastward. Wobbles either side of the track could make a huge difference in terms of conditions felt. These wobbles are due to inner-core dynamics are hard to predict with skill.

  • Track more to the left: easterly winds veer to the south, increasing to hurricane force as Nicole passes (east eyewall)
  • Track more to the right: easterly winds increase to hurricane force as Nicole approaches, suddenly become light and shift to the west, suddenly increase to hurricane force as Nicole passes (eye)
  • Track even more to the right: easterly winds increase to hurricane force and back to the north as Nicole passes (west eyewall)

Wind direction strongly controls who/where sees the most significant coastal flooding due to storm surge. For instance, should winds reach their peak out of the south, then south shore would take the brunt of any storm surge. Similarly, this changes wind exposure as windward hilltops see dramatically higher winds than the sheltered lee-side valleys. It is therefore imperative to both know your exposure and prepare for the scenario that exploits your exposure.

Expect scattered to widespread tree damage and power outages, isolated structural damage (mainly to roofing on elevated and exposed locations or along the track of any tornadoes, and along the coast if an inundating storm surge develops), and isolated flooding from rainfall in low-lying and poor drainage areas. Significant coastal erosion will likely begin to take shape tonight as seas inside the reef become rough, and isolated power outages are likely before dawn tomorrow as winds begin to reach 50 kts in exposed locations.

Nicole Begins Erratic Track

As always stay abreast of the most up to date official information from the National Hurricane Center, and Bermuda Weather Service. The following are my unofficial thoughts:

Yesterday afternoon and overnight, Nicole put on a somewhat unexpected burst of organization and intensification peaking as a category two hurricane with maximum sustained winds estimated near 90 kts (105 mph). This morning however, Nicole has begun to take on the expected erratic track and has weakened due to stronger vertical wind shear. Nicole, however, remains a ‘Potential Threat’ to Bermuda. After drifting to the south and weakening over the next two to three days, Nicole is expected to accelerate northwards toward Bermuda, possibly re-intensifying and has a chance to become a ‘Threat’ to the island by early next week.

[Threat: When effects from any tropical cyclone are possible in Bermuda within 72 hours. – BWS Glossary]

Most recent track forecast for Tropical Storm Nicole. See the latest ‘Local Advisory‘ from the Bermuda Weather Service’s Tropical Products page.

Nicole, after becoming stationary overnight and this morning, is expected to begin a slow drift to the south. In the short term, Nicole has therefore passed its closest point of approach to Bermuda which was about 285 nm south of the island at 6pm yesterday. However, Nicole is still a potential threat to Bermuda at about 290 nm to the south as of today’s midday advisory.

Nicole’s southward drift is expected to pick up pace today and gradually turn back to the west on Sunday as deep layered ridging builds to the north of the storm. Early next week, however, that ridging begins to move east of Nicole as another deep layered shortwave trough approaches the region from the west. This in combination with interaction from Matthew exiting the US east coast is expected to turn Nicole back toward the north. Nicole again approaches Bermuda early next week, possibly becoming a threat to the island by mid-week. The track forecast early next week is still more uncertain than average and it is not clear how Nicole will interact with both the shortwave trough and Matthew in the coming days.

Hurricane Nicole yesterday afternoon rapidly intensifying  with eye feature and symmetric deep convection (left). Nicole after strong vertical wind shear rapidly weakens the cyclone, leaving it with asymmetric deep convection loaded to the south of the storm (right). See latest satellite imagery centered on Nicole here.

In terms of intensity, very strong vertical wind shear is currently weakening Nicole. These strong upper level winds have stripped the organized convection away from the low-level center of Nicole this morning. This has weakened Nicole dramatically from a category two with maximum sustained winds near 85 kts (100 mph) to a tropical storm with winds near 60 kts (70 mph) in six hours.

This strong vertical wind shear is expected to continue to weaken Nicole today to a minimal tropical storm by Saturday. These unfavorable upper winds are expected to persist at least through Monday, limiting Nicole’s intensity. Nicole could degenerate into a remnant low in this time, or could prove again resilient to large scale shear and maintain moderate tropical storm intensity. However, the environment is expected to gradually become more conducive for development as Nicole approaches Bermuda early next week.

The overall atmospheric set up next week is again very uncertain and therefore it is important to continue to monitor the progression of Nicole over the next five days and prepare accordingly should Nicole become a threat to Bermuda.

Nicole and Matthew

As always stay abreast of the most up to date official information from the National Hurricane Center, and Bermuda Weather Service. The following are my unofficial thoughts:

Tropical Storm Nicole

No adverse weather is currently expected from Nicole in the next five days. However, Nicole is forecast to take on an erratic track starting Friday, keeping the storm within the ‘potential threat’ radius (400 nm) for at least the next five days while maintaining moderate tropical storm strength.

[Potential Threat: When the center of a tropical cyclone is expected to pass within 400 nm of Bermuda within 72 hours. – BWS Glossary]

In the next 72 hours, Nicole is expected to come as close as 240 nm to Bermuda. However, both at and after that time there is potential for Nicole to track closer to the island. See the latest ‘Local Advisory‘ from BWS.

Further, the steering patterns that are responsible for Nicole’s erratic forecast track between Friday through Sunday are unstable. That means small changes in the steering pattern will result in large changes in the eventual track of Nicole. Adverse weather related to Nicole will therefore remain a possibility early Saturday, through and beyond Sunday.

Nicole originated from a tropical wave embedded in the inter-tropical convergence zone in the Central Atlantic. The wave tracked northwestward, staying northeast of the Caribbean. It experienced significant vertical wind shear from an upper level low nearby that slowed organization of the cyclone. Yesterday morning, the low became stacked with the axis of the weakening upper level low where vertical wind shear is locally lower, and convection was able to organize allowing a tropical cyclone to form.

On the 12pm forecast from NHC, Nicole will be over sufficiently warm waters and in a regime of gradually increasing wind shear. However, how (un)favorable the upper level winds are depends on the eventual evolution of the steering pattern, which is currently being forecast with lower than normal confidence and therefore, Nicole’s intensity forecast is lower confidence than normal. NHC is forecasting near steady intensity over the next three days, then a slight weakening.

Hurricane Matthew

Hurricane Matthew is currently exiting Haiti and Cuba where locally extreme damage was likely done. Matthew is about to begin a 36 hour track through the Bahamas impacting many of these islands with violent winds, life-threatening storm surge and heavy rain related flooding. Florida is then at threat from Matthew as the hurricane exits the Bahamas. Matthew too has an uncertain long-range track, with a small but non-zero chance for impacts in Bermuda.

4th October 2016, Suomi NPP/VIIRS True Color imagery of Hurricane Matthew over the Gulf of Gonaives and Tropical Storm Nicole ~550 nm northeast of Puerto Rico.

Over the weekend, Hurricane Matthew rapidly intensified into the Atlantic Basin’s first category five hurricane since Hurricane Felix (2007) as it meandered in the eastern and central Caribbean Sea. Matthew then weakened due to a combination of inner core dynamics and some intermittent dry air entrainment, but remained an extremely dangerous category four hurricane.

[The eye of Matthew passed over Buoy 42058. via National Data Buoy Center]

At category four strength, Matthew made landfall in southwestern Haiti near Les Anglais on Tuesday morning, crossed the Gulf of Gonaives, and made a second landfall in eastern Cuba near Baracoa. Near the landfall locations, a combination of violent category four strength winds and significant storm surge likely caused locally extreme damage. Heavy rains, spreading far from the center of Matthew, are responsible for flooding across the Caribbean, particularly in Haiti, Cuba, and the Dominican Republic.

National Hurricane Center 5-day forecast track at 3pm local time showing warnings in effect for Hurricane Matthew. See Latest.

Interaction with land over Haiti and Cuba has weakened Matthew only slightly to a category 3 hurricane. Matthew is currently in the south-central Bahamas. Violent winds and storm surge will make conditions extremely dangerous and locally life-threatening on many of the Bahamas islands as Matthew tracks through the island chain.

Further, Matthew is in a moist environment with low vertical wind shear and is over some of the warmest water in the Atlantic, as a result, Matthew is expected to at least maintain its category three intensity, if not re-strengthen as it moves through the Bahamas over the next day or so.

[Category what? See NOAA’s explanation of the Saffir-Simpson Hurricane Wind Scale]

By late on Thursday, Matthew is expected to be approaching the east coast of Florida as a major hurricane. Between day two and three Matthew is expected to parallel the east coast of Florida before turning sharply to the east on Saturday. However, small changes in the track of this hurricane could bring violent winds onshore, or keep them far off shore leading to an unusually wide range of possible impact scenarios despite a forecast with near average confidence through this timeframe.

After the eastward turn on Saturday, as with Nicole, the forecast becomes much less confident. Right now the most supported scenario appears to have Matthew beginning to turn to the south then west and threaten the Bahamas and Florida once again in the 5-10day range. However, Matthew could also continue eastward and become a ‘potential threat’ to Bermuda. At this time, no adverse weather is expected from Matthew in Bermuda.

Karl Passes with Minor Impact

Tropical Storm Karl failed to strengthen into a Hurricane as it passed Bermuda. Karl’s structure dramatically changed and deep convection waned in the final hours of approach. This was evidenced in aircraft reconnaissance missions that were ongoing into the storm into the early hours of Saturday. The region of peak winds shifted from the northwest quadrant to the southeast quadrant, and the center of the storm was surrounded by a gaping region of moderate winds.

Karl about 85 nm south-southwest of Bermuda with deep convection near the center beginning to organize into an eye-like feature. 1:55am local time.
Karl near closest point of approach, about 45 nm southeast of the island. deep convection redeveloping north and west of the center, but not as organized or as close to the center. 5:58am local time.

Karl passed about 45 nm southeast of the island just before 6am on Saturday with maximum sustained winds near 65mph. Winds around Bermuda peaked later in the morning as Karl moved away and winds backed to the north. Observations show sustained winds generally peaked in the 20-40 kts range with gusts up to 50 kts, particularly in elevated and exposed areas. Further, only these exposed locations saw sustained tropical storm force winds and even then, only in/around gusty showers.

Storm total rains from Karl officially reached 4.71″ at the airport. Automated personal weather stations around the island saw notably lower storm totals and this might be an artifact of measuring methods. Measuring rainfall accurately in tropical cyclones is notoriously difficult because of the accompanying high winds and I would suspect that the official total is likely closer to what actually fell.

Aside from a few delayed business openings, some transportation disruption, and isolated power outages, Bermuda fared well through Karl.

See a preliminary and unofficial list of observations around Bermuda from Wundground and BWS:


Peak Gust

Storm Total Rain

Bermuda Weather Service (Official) 41 kts (47 mph) 4.71″
MAROPS, St. George’s 50 kts (58 mph) NA
Commissioner’s Point, Sandy’s 48 kts (55 mph) NA
Pearl Island, Paget 47 kts (54 mph) NA
The Crescent 45 kts (52 mph) NA
Gilbert Hill, Smith’s 43 kts (50 mph) 1.82″
Magnolia Hall, Smith’s 41 kts (47 mph) 2.39″
Town Hill, Smith’s 41 kts (47 mph) 3.03″
Hinson’s Island, Warwick 41 kts (47 mph) 1.59″
Cardinal, Southampton 41 kts (47 mph) 2.33″
Esso Pier, St. George’s 39 kts (45 mph) NA
St. David’s, St. George’s 37 kts (42 mph) 2.53″
Chaingate Hill, Devonshire (My PWS) 34 kts (39 mph) 2.43″
Wilderness, Smith’s 34 kts (39 mph) 2.22″
McGall’s Bay, Smith’s 33 kts (38 mph) 4.15″
Devon Heights, Devonshire 30 kts (35 mph) NA
Hamilton, Pembroke 30 kts (34 mph) 2.34″
Tucker’s Town, Hamilton 27 kts (31 mph) 3.29″
Moore’s Lane, Pembroke 24 kts (28 mph) 2.28″
Ocean View, Southampton 23 kts (27 mph) 2.36″
Devonshire, Devonshire 18 kts (21 mph) 2.46″