A nervous week awaits: uncertainty still high regarding Matthew

Good afternoon.

There is one big weather story right now and it is Hurricane Matthew. After a period of very rapid deepening on Friday, it topped out as a category 5 hurricane with 160 mph sustained winds. That made it the strongest storm in the Atlantic basin (wind-wise) since Hurricane Felix in 2007. It has since weakened a bit but remains an extremely dangerous storm. It will likely remain intense through the medium range unless it spends an extended period over mountainous regions of Hispaniola or Cuba. When it comes to long-range threats for the east coast, we just have to watch and wait. It will be an anxious week for all of us.

Important points to make

1) If Matthew does head towards our part of the world (the Northeast), it won’t be until late this week into next weekend at the earliest.

2) Computer models are still far apart in terms of potential track and intensity. In fact, confidence decreases dramatically starting around midweek. Much of the energy involving the blocking ridges and incoming troughs is still over the Pacific where observations are extremely sparse. The energy should reach the west coast starting tomorrow and continue to do so through the week.

3) There have been multiple runs by NOAA’s Gulfstream IV aircraft dropping upper-level dropsondes across the western Atlantic and Caribbean Sea to help sample the atmosphere in areas of scarce data. NWS offices are also launching extra weather balloons this week, at least in the eastern areas. Those will hopefully help greatly in solving this puzzle.

4) This is expected to be an extremely dangerous storm in the Caribbean early this week. Parts of eastern Cuba, Jamaica and Haiti may experience major hurricane conditions in coastal areas and large areas of very heavy rainfall. That could lead to devastating flash flooding and mudslides, along with wind damage. It is not out of the question that Matthew could be a category 4 or 5 hurricane at first landfall.

5) While most models keep Matthew east of the Florida peninsula, it will be uncomfortably close. That will likely lead to tropical storm conditions for some areas along the east coast of Florida. Any deviation westward in the track may result in a dangerous hurricane hit for SE Florida. It will likely be a serious storm in the northern and central Bahamas.

Current situation

Water vapor imagery of Hurricane Matthew at 2:45 pm EDT October 2, 2016. It remains a very well organized storm and is growing in size gradually.Water vapor imagery of Hurricane Matthew at 2:45 pm EDT October 2, 2016. It remains a very well organized storm and is growing in size gradually.

Matthew has weakened slightly since yesterday due to wind shear and upwelling, but it remains an extremely dangerous hurricane located about midway between Jamaica and the Guajira Peninsula. After barely moving yesterday, it is slowly moving west to northwest, although with frequent wobbles. That suggests the center of the storm will likely go west of 75°W and perhaps closer to 77-78°W for now. Right now, maximum sustained winds are about 145 mph with a central pressure of 944 mb. 

Given the favorable conditions present and decreasing wind shear, I would expect that Matthew will at least hold its own until landfall in Jamaica, Haiti or Cuba. If it doesn’t go through an eyewall replacement cycle, regaining category 5 status is certainly not out of the question. The Caribbean Sea in this region is very warm with sea surface temperatures as high as 31°C and warm water extending well below the surface. A track farther west would bring Matthew into one of the deepest pools of warm water in the world right now.

One potential wildcard, which will be mentioned below, is that a new disturbance, Invest 98L, has formed well to the east of the Bahamas. It is quite shallow but well defined right now. Some models – notably the ECMWF – suggest that it will become Tropical Storm Nicole, despite being in a hostile environment with high wind shear right now. If it becomes strong enough, it may break down the ridge to the east and open a path out to sea for Matthew. The NHC only gives it a 30% chance of development.

Longer term scenarios

On Friday, I mentioned there were, at the time, five possible scenarios for the long-term prospects of Matthew. I believe that is still the case. Only one of them avoids land altogether after the Bahamas (at least in the foreseeable future, as long as it misses Bermuda), but they have very different outcomes. In each case, the behavior of air masses, ridges and troughs will play a crucial role. Timing is also crucial

Scenario 1: Florida landfall (15% chance)

Early model runs and soundings today suggested that the ridge was stronger than first thought. In other words, the 500mb geopotential height in Miami were determined to be 5,880m when models forecast such to be 5,860m. Although this scenario has no real model support, I still believe it is a reasonable possibility. Some model ensembles come dangerously close to the Florida east coast and there has been a right bias so far (even though doesn’t mean the trend will continue).

In this scenario, Matthew continues on a north-northwest path for the next few days, even northwest at times, as the ridge to the east strengthens. That allows Matthew to push farther west than expected. As a result, it makes landfall in the vicinity of South Florida, probably on Wednesday or Thursday. Some weakening is likely over Cuba and/or Jamaica, but restrengthening would be likely in the Florida Straits. It may either run up the coast inland or just offshore afterward, towards the mid-Atlantic but in a much weaker state. This is similar to Hurricane King in 1950 and Hurricane Cleo in 1964.

Scenario 2: Continued due north path, Carolina landfall (15% chance)
GFS enssemble positions for Matthew on Saturday morning. Notice the spread becomes evident with a couple runs taking Matthew over the North Carolina coast.

GFS enssemble positions for Matthew on Saturday morning. Notice the spread becomes evident with a couple runs taking Matthew over the North Carolina coast.

This scenario is supported by several GFS ensembles, although the main operational runs keep it offshore. The track is affected enough by the ridge to the east to allow Matthew to track farther west than forecast for a longer period of time. The trough to the north does not phase with Matthew, but slows down enough to allow the storm to come onshore in the Carolinas. Most likely, it then returns to the Atlantic in a weakened state due to land interaction.

This would be a devastating scenario for the coastal Carolinas, particularly the North Carolina coast and Outer Banks. Depending on the timing of the recurve or exact track, some impact may be felt in the southern Mid-Atlantic as well. Farther up the coast may feel a weaker storm later, although uncertainty would certainly exist. This scenario is similar to Hurricane Ione in 1955 and Hurricane Bonnie in 1998, albeit with most likely a stronger storm.

Scenario 3: Recurve south of Carolina coast, remains well away from Northeast (25% chance)
12Z CMC vorticity pattern for Saturday morning. The trough cannot capture Matthew, but it does influence enough to turn it out to sea.

12Z CMC vorticity pattern for Saturday morning. The trough cannot capture Matthew, but it does influence enough to turn it out to sea.

The CMC model and many ensembles (especially ECMWF ensembles) have focused on this possibility. The GFDL and HWRF are also leaning this way. There are two possibilities that lead to this (which would be our best case scenario). First, the trough in the Midwest, which could either phase with Matthew or just act as a steering mechanism, keeps moving eastward and the combined movement prevents Matthew from turning back. For that to happen, the ridge to the east cannot build northward as some models have suggested. Another possibility is that 98L becomes a strong Tropical Storm (or Hurricane) Nicole while interfering with the upper level flow enough to open an escape valve.

Any direct impact here would remain well offshore. The beaches will still have very high surf and rip currents, but no land impacts would be expected. It is possible that the storm would recurve again northward into Atlantic Canada (probably Newfoundland) though. Bermuda may also be threatened depending on timing. This scenario is similar to Hurricane Joaquin last year.

Scenario 4: Recurve south of Carolina coast, blocked and drawn into Northeast (25% chance)
12Z GFS vorticity map for next Sunday morning. Unlike in the CMC, the trough actually captures Matthew and draws it northward. It makes landfall in Maine in this model run.

12Z GFS vorticity map for next Sunday morning. Unlike in the CMC, the trough actually captures Matthew and draws it northward. It makes landfall in Maine in this model run.

This is similar to Scenario 3, except a little slower and involving a stronger trough. As supported by the GFS and a scattering of ensembles, Matthew requires an extra day or so to reach a point off Cape Hatteras. As a result of the slower movement, the trough and Matthew essentially combine, with the hurricane phasing with the trough and maintaining (or even increasing) its intensity through baroclinic forcing. That draws Matthew northward or even northwest, turning it into the Northeast coast (most likely in New England but even a hit near Long Island or New Jersey cannot be completely ruled out).

Obviously, this would be an extremely dangerous scenario. It is far too soon to pinpoint any potential impacts, but the fact that this possibility is on the table makes it clear that we all need to monitor Matthew closely. This scenario is similar to the 1938 Long Island Express and Hurricane Sandy in 2012.

Scenario 5: Ridge rebuilds, stalls out (10% chance)
12Z ECMWF run for Saturday morning showing heights and pressures. Notice Matthew is still so far south, with a weak trough to the north that doesn't reach it, that it essentially stalls out.

12Z ECMWF run for Saturday morning showing heights and pressures. Notice Matthew is still so far south. Being surrounded by ridges, with a weak trough to the north that doesn’t reach it, allows it to essentially stalls out.

The ECMWF model – long the most reliable tropical model – continues to go against the grain. It suggests a very slow motion through the Bahamas, requiring all this week just to reach the northern islands. As a result, the trough cannot reach Matthew and a ridge rebuilds just to the west over the Southeastern US coast. It results in an erratic motion off the coast, possibly with looping, as it is blocked by a steering ridge to the east and a blocking ridge to the west working in opposite directions and no real weakness to the north or east.

All this does is extend the anxiety. The key will be when either the next trough digs down, or when the ridge breaks down on any side. It could go just about anywhere, although upwelling may become such an issue that it may weaken the storm eventually. Any such movements would be beyond forecast range. This scenario is similar to Hurricane Felix in 1995.

Conclusion

 

These are uncertain times right now. Matthew is now within forecast range, but the possibilities remain in a wide range. It will still take time to diagnose the ridges and troughs, which are critical in a blocking pattern. This complex pattern means that slight changes in track or timing can greatly affect the outcome. The risk to the east coast is definitely there, but the area cannot be pinpointed. Certainly we can’t predict any impacts this far out. All this week, keep an eye in the tropics.

I will probably have daily blogs this week as long as it is a potential threat.

Forecaster Craig Ceecee – @Ceecee_Wx

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