A rapidly intensifying low pressure system made its way into the Atlantic on Tuesday, 11 February 2020 and quickly grew into a powerful extratropical cyclone producing hurricane force winds by Thursday, 13 February 2020. By 0600 UTC on 14 February 2020, the low bottomed out with a minimum low pressure of 929mb. This system deepened by more than 40 mb in 24 hours during its rapid intensification phase, classifying it as a “bomb” cyclone. It tracked north towards Iceland where it caused hurricane force wind gusts, the highest gust, although terrain enhanced, reached 159 mph (https://www.severe-weather.eu/recent-events/near-record-wind-gusts-255kmh-hafnarfjall-iceland-mk/). These gusts were recorded on the leading edge of the cyclone where the cold conveyor belt north of the occluded front in the N-NE quadrants played a role.
This intense extratropical cyclone was closely followed by another cyclone (named Dennis by the UKMet office) rapidly intensified during the day on 14 February 2020 deepening by 40 mb in 24 hours, classifying it as another bomb cyclone. This system is following a similar path as the previous cyclone, capitalizing on the favorable baroclinic environment left in the wake of the first cyclone.
In the RGB Airmass imagery (above) from GOES-16, it is clear that there is also a large potential vorticity anomaly (red shading) upstream of the system, originating from a trough over the eastern United States. This inflow of potential vorticity into the storm is aiding the rapid intensification of the system. This system deepened to 920 mb as of the Ocean Prediction Center (OPC) 1800 UTC analysis on 15 February 2020. Hurricane force winds have been sampled by ASCAT scatterometers and by aircraft in the early morning hours of 15 February 2020 with maximum winds of 94 kt!
The above ASCAT and Altimeter images from ~1700-1745 UTC on 15 February 2020 show winds in the primary 920 mb low (south of Iceland) still at hurricane-force (>65 kt) with significant wave heights near 42 ft in the southeast quadrant. Meanwhile the older, lee-side low that was part of the 13 February 2020 storm is still exhibiting winds of 50-60 kt, aided by a barrier jet in eastern Greenland and a tip jet near the southern tip of Greenland. The altimeter readings near this latter storm were 30-42 ft (note that it’s possible higher waves (~50+ ft) were in the vicinity of both storms at this time).
These latest ASCAT and Altimeter passes show the 922 mb low (as of the 0000 UTC 16 February 2020 OPC analysis) has started to fill (weaken slightly) with plenty of storm-force wind barbs and significant waves still over 40+ ft, though higher winds of 65+ kt and waves over 50 ft are most likely not sampled.
We will have a more detailed recap of this past week’s stormy north Atlantic in the coming days, so please stay tuned.
The tropical Atlantic has been putting on quite the show over the last couple of weeks of Hurricane Harvey (Category 4). . .I’m sure you heard of that one, followed by Irma (Category 5), Jose (Category 4), and Katia (Category 2). Katia made landfall last night in Mexico and now we continue our focus on Irma and Jose. Why is it so active? A few reasons: warm ocean (sea surface temperature and high ocean heat content), lack of a true El Nino Southern Oscillation (ENSO) signal, though it looks like a weak La Nina, little to no shear throughout much of the basin, a lack of dust from the Sahara, and a strong Azores high. Oh yeah, on top of that, we have the Madden-Julian Oscillation (MJO) more or less stuck in favorable phases for the Atlantic (8, 1, 2, 3) and forecasts suggest that stays in place for a while.
ECMWF MJO verification and forecast courtesy of the Climate Prediction Center (CPC). Click here to open in a new window.
GEFS MJO verification and forecast courtesy of CPC. Click here to open in a new window.
One product I noticed in use at the Ocean Prediction Center (OPC) on Friday, 09/08/17 was the GOES-16 Daytime Convection RGB, so I thought this would be a nice opportunity to show you all three current Atlantic systems with a comparison to the 10.3 µm “clean” channel.
GOES-16 Daytime Convection RGB of Hurricane Irma valid 1100 UTC to 2300 UTC on 09/08/17. *Preliminary, Non-Operational Data* Click here to open in a new window.
Note the bright yellow coloring that highlights, new convection with smaller ice particles indicating strong overshooting tops in the outer rainbands, while the main central dense overcast (CDO) surrounding the eye also gets brighter. This indicates that after the eyewall replacement cycle ended, the new eyewall started to contract and strengthen (winds at this time were 155 mph, but shortly after this strengthened to 160 mph.
GOES-16 10.3 um “clean” infrared window channel similar to the previous animation of Hurricane Irma. *Preliminary, Non-Operational Data* Click here to open in a new window.
Notice that the 10.3 µm “clean” window shows us the brightness temperature of the coldest cloud tops. Although you can see the new overshooting tops, as those thunderstorms rotate around the CDO, it gets more difficult to identify the newer, important convection.
GOES-16 Daytime Convection RGB for Hurricane Jose valid 1000 UTC to 2045 UTC on 09/08/17. *Preliminary, Non-Operational Data* Click here to open in a new window.
By contrast, notice how compact Hurricane Jose became as it strengthened to a 150 mph Category 4 hurricane on Friday (09/08/17). Again, the beginning of the animation shows plenty of yellows that indicate new convection, wile the older convection fades to oranges, then reds. Also notice how the CDO becomes more yellow as the eye becomes cleaner and the storm takes on a more donut structure, even with the strong outflow channel to the northeast that makes the storm look lopsided. Could this RGB be helpful in identifying CDO changes? Or help with indicating eyewall replacement cycles (ERCs) in conjunction with microwave imagery?
GOES-16 10.3 um “clean” infrared imagery similar to the previous animation of Hurricane Jose. *Preliminary, Non-Operational Data* Click here to open in a new window.
Again, to contrast the Daytime Convection RGB, the above 10.3 µm animation shows very cold cloud tops, but the newer convection starts to blend in with the CDO over time. Do you see other differences?
GOES-16 Daytime Convection RGB of Hurricane Katia valid 1200 UTC to 2357 UTC on 09/08/17. *Preliminary, Non-Operational Data* Click here to open in a new window.
Finally, Hurricane Katia was very small in comparison with the other two hurricanes, but notice there are differences in the intensity of the convection on Friday (09/08/17). What do you see in the imagery? There are less yellows than in Irma or Jose, yet the storm intensified to a Category 2, 90 kt (105 mph) hurricane prior to landfall on Friday evening. The warming clouds and less cold, newer convection may have been due to dry air entrainment due to the close proximity to mountainous land nearby and a weak trough to the north.
GOES-16 10.3 um “clean” infrared imagery similar to the previous animation of Hurricane Katia. *Preliminary, Non-Operational Data* Click here to open in a new window.
How does the 10.3 µm imagery above contrast with the Daytime Convection RGB?
So, what is steering Irma? What about Jose and Katia? Well, I’m glad you asked. . .
GOES-16 Air Mass RGB image valid at 0900 UTC 09/09/17. *Preliminary, Non-Operational Data* Click here to open in a new window.
The GOES-16 Air Mass RGB image (courtesy of NASA SPoRT) above with my crude drawings show a rough idea of the players affecting the steering flow around the three hurricanes. Katia has made landfall as it was pushed southwest due to the old cold frontal boundary (responsible for the cool air in most of the country) along with a disturbance highlighted in the yellow circle. This disturbance will close off over the Tennessee Valley area and help to pull Hurricane Irma north, then northwestward in the next 48 hours. Finally, Jose (east of the Lesser Antilles) will be pulled north through a weakness in the ridge due a weakness created by the Tropical Upper Tropospheric Trough (TUTT in the yellow “T”) to the northeast and Irma’s broad circulation. Since the current trough over the northeast U.S. moves east/northeast and the central Atlantic TUTT remains stationary, Irma gets left behind in the southeast U.S., but weakening after landfall, while Jose gets left behind and may perform a tight anticyclonic loop before “possibly” moving northwest. We’ll deal with Jose later. . .
I have included the GOES-16 Air Mass RGB and 7.3 µm low-level water vapor animations below so you can get a better feel of the overall pattern.
GOES-16 Air Mass RGB animation valid 0800 UTC 09/08/17 to 0900 UTC 09/09/17. *Preliminary, Non-Operational Data* Click here to open in a new window.
GOES-16 7.3 um low-level water vapor animation valid from 0800 UTC 09/08/17 to 0715 UTC 09/09/17. *Preliminary, Non-Operational Data* Click here to open in a new window.
My final thoughts. . .please follow the National Hurricane Center for official track and intensity guidance on Irma and Jose. I have included the track forecasts below.
The 8 am EDT NHC track forecast for Hurricane Irma. Click here to open in a new window.
The 8 am AST NHC track forecast for Hurricane Jose. Click here to open in a new window.
During the overnight hours of March 19-20, 2017, an amplifying upper level shortwave moved off the Mid Atlantic coast and led to the rapid development of a mesoscale oceanic cyclone across the Gulf Stream east and southeast of Cape Hatteras. The upper level feature moved south and southeast along the backside of a deep upper level long wave trough near 68W. The global models including the GFS and ECMWF were not well initialized with the upper level shortwave and consistently, over the previous several model runs, were only indicating a weak trough would develop at the surface. Conversely, the 4km NAM and HRRR were each showing surface low development and significantly higher associated surface winds than shown by the coarser global models. OPC forecasters had been carrying storm warnings across a few offshore zones through 00 UTC March 20, 2017.
The GOES-16 water vapor imagery, including the 6.9 um mid-level and 6.2 um upper-level, suggested that the mid/upper shortwave was more amplified than initialized by the global models. The feature was also apparent in the GOES-16 7.3 um lower-level water vapor imagery, indicating it may be vertically stacked or at least extend through the lower levels. The three water vapor channels alone indicated there was likely adequate forcing through the upper and mid levels, and even into the lower levels, to support the development of a surface low. However, the low level circulation analyzed in the GOES-16 3.9 um shortwave infrared imagery confirmed the presence of the surface low. In addition, the enhanced baroclinicity the system encountered as it tracked across the Gulf Stream likely played a big role in the storm’s intensification. The sea surface temperature (SST) gradient along the north wall of the Gulf Stream can be seen in the GOES-16 3.9 um shortwave infrared animation.
GOES-16 6.2 um upper-level water vapor animation valid 2102 UTC 19 March 2017 – 0902 UTC 20 March 2017. *Preliminary, Non-Operational Data* Click here to open in a new window.
Upon reviewing the GOES-16 imagery and evaluating the most recent model guidance, the overnight OPC forecaster extended the storm warning through the night period, and also expanded the warning to include the outer mid Atlantic offshore waters. The significantly improved temporal and spatial resolution of the GOES-16 imagery, along with the additional water vapor channels, allowed forecasters to better diagnose the strength of the upper level shortwave and also, the presence of the surface low, which then gave forecasters more confidence in amending the warnings. Even as the both the upper level feature and the surface low appear to shear and weaken in the three GOES-16 water vapor channels and 3.9 um shortwave infrared band around 06 UTC, there was a ship which reported gale force winds (35 kt) at 06 UTC well southwest of the surface low.
Thanks for reading!
James Clark (OPC) and Michael Folmer (CICS)
“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”
Last week I posted on the very active tropical Pacific Ocean with four storms occurring simultaneously. Tropical Cyclone Pam (17P) made a devastating visit to the island nation of Vanuatu as a Category 5 (145 kts or 165 mph) cyclone and has since joined the westerlies after passing near New Zealand as a much weaker system. Currently, the majority of the region has quieted down some, but Tropical Cyclone Nathan (east of Queensland) and Tropical Storm Bavi (West Pacific) are still active, while Tropical Cyclone Olwyn dissipated after making landfall in Western Australia. Jim Kells (OPC) compiled a few animations that show the evolution of all four tropical cyclones starting on 03/08/15. The imagery is courtesy of the MTSAT-2 satellite and we are eagerly anticipating the new Himawari-8 satellite data over the next few months.
MTSAT-2 Infrared satellite animation of the four tropical cyclones developing in the tropical Pacific and Indian Oceans valid from 03/08/2015 – 03/16/2015.
MTSAT-2 Infrared (enhanced) animation similar to the previous animation.
MTSAT-2 Water Vapor animation valid from 03/08/2015 – 03/16/2015.
So why did it suddenly get so active?
NCEP GEFS forecast of the Madden-Julian Oscillation (MJO) courtesy of the Climate Prediction Center (CPC).
The MJO is currently near or at a record amplification in Phase 7 and as it swung through Phase 6 to 7, a strong westerly wind burst developed near the equator, while there was enhanced upward motion or ventilation at 200 mb. This has also been coupled with a sudden drop in the Southern Oscillation Index (another ENSO indicator).
Empirical Wave Propagation forecast for the next 40 days courtesy of CPC.
According to one forecast (above), the Empirical Wave Propagation forecast shows a return of favorable tropical cyclone formation conditions (green shading) appearing in the same region from the end of March into early April (the season typically winds down in the Southern Hemisphere after April).
Sea Surface Temperature animation from 12/24/2014 – 03/11/2015 in degrees Celcius courtesy of CPC.
Sea Surface Temperature Anomaly animation from 12/24/2014 – 03/11/2015 courtesy of CPC.
Finally, notice that this region is where the warmest SSTs reside in the tropical Pacific, along with the strongest warm anomalies. This is typical of a Modoki El Nino where the warmest conditions are in the Nino 3.4 region or near the Dateline. Also notice how the water near the coast of South America is colder than normal. This shows a mixed signal and makes one wonder whether El Nino conditions will be maintained or expand east with time. . .
From September 20 through September 23, 2014, the Ocean Prediction Center (OPC) was monitoring the development of the season’s first hurricane-force extratropical storm in the East Pacific. Models were suggesting a marginal hurricane-force wind event would unfold well west of the Pacific Northwest, near 140W longitude, north of 40N latitude. OPC is routinely using satellite data to monitor and forecast these strong ocean storms. On this particular event, OPC forecaster James Kells collaborated with Michael Rowland and David Kosier on if and when to pull the trigger on the hurricane-force warning.
GOES-15 6.5 um water vapor animation showing the evolution of the hurricane-force low.
The above animation shows the evolution of the hurricane-force low, with an eye-like feature evident near the end of the loop. By 1200 UTC on the 23rd, it was forecast to develop hurricane force winds (64 knots or greater) just west of Oregon near 140W. During the production of the 1200 UTC OPC Surface Analysis, there was question of whether or not the winds had reached hurricane force intensity. The ASCAT pass from ~0600 UTC showed a large area of 50-55 knot winds in the strong cold advection south of the low center, and the GFS model indicated that the system was still developing. The GFS 0-30m boundary layer winds also indicated a very small area with hurricane force intensity.
Advanced Scatterometers A and B overlaid on GOES-15 Infrared imagery showing storm force winds at ~0600 UTC on 09/23/14.
The 1130 UTC MODIS RGB Air Mass product was timelier, and it showed an area of downward momentum south of the low with the deep purple shading. The corresponding water vapor image was less clear with upper level moisture obscuring the downward motion just beneath it. In addition, there were no surface reports south of the low center as there were no buoys moored nor drifting in that vicinity. Furthermore, most ships were aware of the danger and navigated away from the region neglecting the possibility of a surface report in the area of question.
Aqua MODIS RGB Air Mass image from 1130 UTC on 09/23/14.
A cross-section of the 1200 UTC 09/23/14 GFS model potential temperature and dew point temperature was taken through the low center in order to analyze the depth of the stratospheric intrusion, and also to gauge the magnitude of the downward momentum. It showed a deep stratospheric intrusion to roughly 500 hPa, and it corroborated the strong downward momentum indicated by the imagery. The RGB Air Mass image showed the intensity of the downward momentum through the red/purple coloring and gave a good indication of the stronger winds aloft mixing down toward the surface. The imagery increased confidence with classifying the system as a hurricane force low.
The 1200 UTC 09/23/14 GFS vertical cross-section of potential temperature and dewpoint showing the downward transport of drier air associated with the tropopause fold.