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Steven Copertino

Tropical Depression Sixteen Forms Off the Coast of Nicaragua, Likely to Strengthen

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Good Evening! 

The active hurricane season of 2017 continues on with yet another system developing, this time down near Nicaragua. Around two weeks ago, we highlighted that there was at least a moderate chance that the increased thunderstorm activity, below-average wind shear, and above normal sea surface temperatures would lead to some kind of tropical system during the first week of October. Like clockwork, we had a very large tropical wave move across the central Caribbean with an associated upper low just to its west. This greatly increased shower and thunderstorm activity over the area and began to lower pressures. Thunderstorms began to consolidate and yesterday the National Hurricane Center designated a small area of low pressure north of the Panama coast embedded in these showers and thunderstorms as Invest 90L  with a high chance of development. Earlier today, surface observations and satellite data showed that the system had become sufficiently organized enough to be classified as the sixteenth tropical depression of the season with winds around 35 mph.

A little after one o’clock or so, the hurricane hunters flew into the depression to get a better idea of the systems strength and its overall structure. They did not find anything overly impressive, but they did find that the system did have a relatively well-organized center with winds around 35mph. The pressure was down to 1006mb, which is quite typical for these types of monsoonal depressions during the month of October. Since that time, the depression has not changed very much, but remains well organized with multiple curved bands and low level spiral bands present around the circulation. Convection is not all that deep at the moment, but this is to be expected during the afternoon hours with peak heating. As the sun sets and temperatures begin to cool, the temperature differential between the ocean and the cooler air aloft should spark numerous thunderstorms that should help the system begin to become better organized.

Visible satelite imagery of Tropical depression 16 just off of the Nicaraguan coast this evening with 35 mph sustained winds (RAMMB CIRA)

Visible satelite imagery of Tropical depression 16 just off of the Nicaraguan coast this evening with 35 mph sustained winds (RAMMB CIRA)

The depression should continue to gradually move towards the coast of Nicaragua over the next 12-24 hours, likely strengthening to a tropical storm in the process. This afternoons SHIPS text (which is a guide for intensity for cyclones) showed a rather significant chance that TD16 will rapidly intensify over the next 24-48 hours, with up to a 60% chance of the system increasing by 55 knots in the next two days. We will have to closely monitor this system over the next day or so to see how convection develops and organizes over the center. Since the system has a relatively small center already, it would not take much in the way of deep convection for the system to be able to begin to rapidly intensify over the extremely warm waters of the Caribbean and take advantage of the very strong Oceanic Heat Content below the system. History is also on the side of this system, as some of the most intense hurricane on record have intensified in the same area that this system will be tracking.

Regardless, it is likely that this system will be a moderate to strong tropical storm by the time it interacts with Nicaragua tomorrow afternoon. The system should exit central America tomorrow evening, and should be able to retain tropical storm strength as it reemerges over the Caribbean. Initially the cyclone will be over relatively shallow waters near the coast, but as it continues to accelerate north it will begin to encounter some of the warmest and deepest oceanic heat content in the world. This point will be crucial, as we will have to see if the system has a stable enough core post lander interaction. Upper level conditions will be quite favorable, with a large upper level low back away from the system off to the north and west, which should create a nice poleward outflow channel. This will allow for the system to effectively transport latent heat from the center of the storm. At this time, it seems that a strong tropical storm or minimal hurricane will be likely by Friday afternoon, when the system is nearing the Yucatan Peninsula.

Map showing the forecast points for TD16 with Oceanic Heat Content in the background. The yellow and orange values are quite high, and support a strong system.

Map showing the forecast points for TD16 with Oceanic Heat Content in the background. The yellow and orange values are quite high, and support a strong system.

TD16 should either pass over the Yucatan or just east by Friday evening, and eventually make its way into the Gulf of Mexico. At this point, the intensity of the storm will be highly dependent on the structure of the system, but if the system remains healthy and the core is not too disrupted from the Yucatan, then it appears quite possible that the system could enter the Gulf as a low-end Category 1 hurricane-possibly stronger if it gets its act together earlier in time. After this point, it becomes pointless to speculate on intensity once the system reaches the central Gulf by Friday, but the global models seem to indicate that there is good chance that upper level conditions will remain conducive for at least some intensification as the system approaches the Gulf Coast. TD16 should be nearing the Gulf Coast as early as Sunday morning, but the exact landfall point will likely not be known until Friday or so. For now, I would say that points from the “Big Bend” of Florida to the central Louisiana coast should keep a close on the progress of this system over the next few days as the overall intensity forecast for this system remains complicated and could change in a moments notice.

We will have an update on this system and its potential impacts for the Northeast later in the week!

This afternoons HWRF model showing TD16 steadily strengthening into a strong hurricane before landfall along the Gulf Coast

This afternoons HWRF model showing TD16 steadily strengthening into a strong hurricane before landfall along the Gulf Coast

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Have a great night!

Steve Copertino

Steven Copertino

Maria Meandering Offshore, Summer Temps Return In the East!

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Good Evening!

The tropics are still quite active with both Hurricane Maria and Lee out over the Atlantic this evening, with both storms at Category 1 intensity. Back on Friday, we talked about how Lee was located in a very favorable environment for quick strengthening due a favorable baroclinic background in addition to its very small structure. Lee did in fact intensify quite quickly the past weekend into a strong Category 1 hurricane with winds around 90 mph over the open-Atlantic, thousands of miles away from land. Lee has been a very interesting storm to follow, as it resembles more of the norm that we have seen over the past few hurricane seasons where a disturbance or weak storm will wait until reaching around 20-25N before really beginning to strengthen. Regardless, Lee should remain in a relatively favorable environment for the storm to at least sustain itself for another two days before shear dramatically increases and sea surface temperatures become quite cool. Lee should eventually become absorbed by a larger non-tropical system in the north Atlantic in about 5 days as it gradually heads north at around 10 mph.

Satellite Imagery of a very small Hurricane Lee with winds up to 85 mph

Satellite Imagery of a very small Hurricane Lee with winds up to 85 mph

Closer to home, we have Hurricane Maria located off of the southeast United states with winds of around 80 miles per hour. Maria has been exposed to the cool wake left behind by Hurricane Jose which was over the same region just about a week ago. This cool wake has led to the storm losing its once very deep convection and this has in turn led to the inner core of the storm to spread out into a larger and broader circulation with tropical storm force winds extending far away from the center. This is causing a large section of the east coast to experience very dangerous rip currents and increased wave action.  Maria should continue to move northward over the next couple of days as it round the side of a large area of high pressure over the western Atlantic. Maria’s forward speed should also remain rather sluggish as well due to the large area of mid level ridging over the Northeast.

Maria will come close enough to the Outer Banks of North Carolina by tomorrow afternoon and evening that tropical storm force winds may occur with any bands of rain that may try and work their way close to the islands. As Maria is just off the coast of North Carolina, a deep trough coming in from the west will begin to affect the hurricane and cause the storm to speed up a bit. As it speeds up, the trough will also pick Maria up and begin to kick it out to the northeast, and finally away from land. At this time, Maria is not a huge threat to land other than rip currents and gusty winds in the Outer Banks, but please follow your local National Weather Service and the National Hurricane Center for more information on this storm over the next few days. Also, please head any warnings at the beaches this week as rip currents and strong waves could possibly be life-threatening if not taken seriously!

GOES 16 loop of both Hurricanes, Maria and Lee churning out over the Atlantic today (Credit: NASA/SPort)

GOES 16 loop of both Hurricanes, Maria and Lee churning out over the Atlantic today (Credit: NASA/CIRA)

Summer-like Weather Returns…For How Long? 

The area of strong mid level ridging parked over much of the Northeast continues to bring very warm temp[temperatures for this time of the year to the region, with many stations across the area seeing highs in the upper 80’s to lower 90’s-which is around 10-20 degrees above normal for this time of year. This area of ridging will also provide clear skies and prevent any chances of rain over the next few days, despite an increase in dewpoints over the past thirty-six hours. Temperatures through Wednesday should remain in the middle to upper 80 range, with some locally higher temperatures expected away from the coast. With the increased low level moisture, there will also be a risk for fog each evening, which could reduce visibility down to less than a quarter-mile at times. Lows will be generally mild through the middle of the week, with temperatures remaining in the middle 60’s to lower 70’s.

Later in the week, a large mid level trough will swing down from Canada and kick out the ridge that has been providing the area with summer-like temperatures for the past few days. This trough should deliver a nice cool-down as the Canadian air really begins to settle in towards the start of the weekend. Highs will likely fall back into the 70’s across much of the area, with low in the 40’s and 50’s, which should make things feel a lot more like fall. As of right now there does not appear to be any significant precipitation events over the next 5 days, but will be monitoring any trends over the next few days!

There are some indications in the medium range guidance that more summer-like temperatures may try and return to the east for the first week of October, but we will cover that in more detail later this week as the exact details and timing become more clear!

ECMWF model showing a mid level trough working into the Northeast this weekend with another ridge hot on its heels (Accuweatehr Pro)

ECMWF model showing a mid level trough working into the Northeast this weekend with another ridge hot on its heels (Accuweatehr Pro)

For more information and posts like this one, make sure you sign up for Premium Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a great evening!

Steve Copertino

Steven Copertino

Maria Finally Departs the Caribbean and Jose Fades. Whats Next?

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Good Evening

Back on Monday we highlighted the potential for Maria to become an extremely dangerous Category 4 or even 5 Hurricane before reaching the small island of Dominica in the Lesser Antilles, and unfortunately that is exactly what happened. Maria rapidly intensified into a Category 5 hurricane with 160 mph winds just before making landfall on the small island, and then preceded to head from SE to NW, leaving the entire island in its core for at least three hours. The storm was the second Category 5 land falling hurricane this season, tying the 2007 with Dean a Felix. Details are still very spotty, but the pictures, video, and first-hand accounts of Dominica are heart-breaking. Most, if not all of the homes on the island have suffered severe damage, with some houses being completely destroyed. Due to the topography of the island, devastating mud slides and land slides were common, which swept away homes, roads, and well-built concrete structures. Its hard to believe that we’d have a storm that would rival the total devastation that Hurricane Irma caused just a few weeks ago, but we could be looking at yet another situation  where an entire island community has seen complete devastation. With the peak of the Cape Verde season quickly coming to a climatotlogical end, we should see the frequency of storms impacting this region begin to wind down, but I would not be surprised to see one or two more systems during the month of October given the active state that we are currently in.

Damage from Hurricane Maria when it hit the island of Dominica as a Category 5 hurricane with winds of up to 160 miles per hour (Credit: The Guardian)

Damage from Hurricane Maria when it hit the island of Dominica as a Category 5 hurricane with winds of up to 160 miles per hour (Credit: The Guardian)

Due to the high, mountainous peak of Dominica and the amount of time that Maria spent traversing the island, the inner eyewall of the storm become disrupted and fractured, but not for long. On Tuesday the storm began to rapidly regain strength after dropping to a Category 4 hurricane. Recon missions throughout the day found that the storm had an incredibly compact eye of around 5-8 nautical miles and the winds rose from 155 mph to 175 mph during the course of the day, with the pressure falling to an incredible 908 millibars, making the storm the tenth strongest on record for the Atlantic basin.

Recon also released numerous dropsonde instruments which provide a vertical profile of various locations in the storm, and some of these probes happened to measure extreme winds of around 190-195 mph at the surface, but it is not certain whether these were instantaneous gusts or actually representative of the storms strength. Regardless, the storm began to approach the US Virgin islands late in the day on Tuesday and into the evening. Very deep convection began to develop quite rapidly around the center of the storm, and before long, concentric eye walls began to develop. This marked that the storm was about to attempt an eyewall replacement cycle before hitting Puerto Rico. It was clear that the storm would have issues completing this process and then intensifying once again due to the storms intensity and the size of the outer eyewall, but it also signaled for new dangers to arise. The storms wind field grew quite substantially as it approached Puerto Rico early Wednesday morning, causing the carious weather stations to be blown apart in addition to both weather radars on the island.

The storm raged ashore with winds in the 155 mph range, making Maria a strong Category 4 hurricane on the Saffir-Simpson scale. Maria went on to produce prolific flooding, wind damage, and cut a path of carnage across the island that would send all of its inhabitants into darkness as all of the power facilities went down during the storm. Details are also still rolling in slowly on the extent of the damage to the island, but it may be safe to say that the Puerto Rico that existed before Maria is no longer there. Estimates say that power may not be restored to some portions of the island for possibly up to 4-6 months. Additionally, much of the infrastructure will need to be rebuilt, which will be a daunting task in of itself. The next few weeks and months may be quite rough for the locals, but with resilience and endurance the people of the island will be able to overcome this disaster and restore their home to levels greater than before Maria.

GOES 16 imagery of Hurricane Maria making landfall on the island of Puerto Rico with winds of up to 155 miles per hour

GOES 16 imagery of Hurricane Maria making landfall on the island of Puerto Rico with winds of up to 155 miles per hour

Maria has since left the Caribbean, and land interaction along with an increase in vertical wind shear have been affecting the system. The storm weakened down to a Category 2 on Thursday, but has since regained some strength and is now a 125 mph Category 3 hurricane. The storm is currently located very close to the Turks and Caicos, producing winds up to tropical storm force on the islands along with torrential rainfall as it slowly heads NNW at around nine miles per hour. Maria should keep this heading over the weekend and into the early portion of next week, but some key aspects of this forecast remain in question. While it is quite likely Maria misses the United States, the American model has been trending strong with the riding out ahead of Maria in the past few runs, bringing the storm precariously close to the Outer Banks of North Carolina. Again, such a solution looks unlikely right now, but with the remnants of Jose still meandering around, we truly will not know just how close the storm passes to the east coast before it makes its famed passage out to sea.

Trend loop of the GFS model showing the westward trend over the past 5 runs (Courtesy of TropicalTidbits)

Trend loop of the GFS model showing the westward trend over the past 5 runs (Courtesy of TropicalTidbits)

So What Else? 

Well, we have the remnants of tropical storm Jose which has finally become post-tropical after 70 advisories by the National Hurricane Center. For reference, this storm has been ongoing since Hurricane Irma was north of Hispaniola! The remnants of this storm should gradually dissipate over the next few days and really should not be much of a threat besides increased wave action and showers. Elsewhere, Tropical Storm Lee has come back to life after shedding about three different low level circulations over the past three days and is located well out in the open Atlantic, just east of a large upper level low. Lee is an extraordinarily small system and is reminiscent of Hurricane Michael from 2012 in that of it is relying heavily on baroclinic process to form convection and strengthen. Given its size and the upper level conditions, I would give the storm a higher than normal odds of becoming a small hurricane over the next few days.

Lastly, our eyes turn to the western Caribbean as the month of September begins to fade. Medium and long range models are showing that this area of the Atlantic basin may become much more active during the next few weeks as a large area of upper level divergence sets up right over extremely warm sea surface temperatures of around 31-32 Celsius. This upper level divergence over very warm waters would promote a large amount of deep convection to form, which could eventually lower pressures in the Caribbean and cause a tropical system to form. This is all at least 8-12 days out at this point, but the signals are there that we should begin to monitor this region for potential tropical cyclone development as we near the beginning of October.

I will have a full update on Maria and any other threat that may pop up on Monday!

ECMWF model showing large scale rising over the western Caribbean in about 10 days. Conditions could become quite favorable for tropical cyclone genesis by this time.

ECMWF model showing large scale rising over the western Caribbean in about 10 days. Conditions could become quite favorable for tropical cyclone genesis by this time.

Have an excellent weekend!

Steven Copertino