Convective coverage and intensity has increased with Beryl this morning, though her center is still not covered. As expected, the Gulf Stream has allowed convective bands to develop and strengthen the circulation. Although this morning’s recon plane did not find a change in central pressure (998mb), they found that winds had increased to around 60mph. This increase is due to the fact that Beryl had no thunderstorms yesterday, and the new ones she has today have tightened the circulation and the pressure gradient, thus increasing the wind speeds despite no change in central pressure. This type of organizational intensification will be the main source of any further strengthening of Beryl before landfall. Visible satellite imagery reveals a dry slot in the NW quadrant of the storm where cooler shelf waters are causing convective bands to dissipate, illustrating the region where Beryl will cease strengthening prior to landfall as she moves over it. Landfall will occur this evening just south of Jacksonville, Florida, and any further strengthening should be slight. Overall, her peak intensity and landfall location look like they will be in perfect agreement with my forecast from before she was named.
I discuss in the video why Beryl is fully tropical and should be classified as such by the NHC before landfall, but we will see what they decide. If they don’t reclassify it, I think it will get a second look in the post-season. Right now what title they give it doesn’t change the impacts to the coast.
The main story with Beryl will be the beneficial rainfall that she will provide to central-northern Florida and Georgia. As promised, rainfall can be found all around the circulation, and it will provide drought-relief for a wide swath following landfall. Unfortunately, the trough that is eroding the ridge to the north of Beryl will be recurving her to the NE or ENE tomorrow and Tuesday, taking her along the coast of the Carolinas, possibly offshore, and the shearing from the trough may keep most of the rainfall offshore for those areas, but some relief is still possible. Most models suggest that Beryl will redevelop into a tropical storm off of the outer banks of North Carolina, but she will be no threat for a second landfall.
After Beryl, the Atlantic should turn quiet for at least the next two weeks, and I think we will have to wait until after June 15th for any more significant threats for tropical development. May was extremely active, but the official season will start slow. I will be posting more on the reasoning behind that after Beryl is out of our hair.
We shall see what happens!
Subtropical Storm Beryl formed yesterday as expected, and is now a well-defined area of low pressure due east of Savannah, Georgia. Thunderstorm activity is a bit lacking this morning, and the circulation is a bit naked. The reason Beryl looks worse today is because she has become vertically stacked beneath the upper low that was to her west yesterday, and thus she has lost baroclinic support, and is being forced to use tropical processes (thunderstorms) to maintain herself. Ship reports indicate she hasn’t really weakened, but she definitely has not strengthened since last night either. A recon plane will investigate her in a couple of hours to better gauge her strength. As discussed previously, the limiting factor for Beryl is dry air being entrained from her west. She has more moisture available than Alberto did, but it will still be difficult for her to sustain heavy convection over her center. Beryl will be moving over the Gulf Stream tonight, with SSTs 1.0-1.5C warmer than what she is currently over, and that should help her increase convective activity. Popcorn convection bands are apparent in visible imagery wrapping in towards the center, indicating that the environment is still unstable enough to allow thunderstorm development if enough moisture convergence is present. Again, warmer waters will likely help that later today.
Beryl should reach peak strength prior to landfall, and then weaken slightly just before landfall as she moves over the cold shelf waters off the coastline. Beryl’s peak intensity should still reach near 60mph if she can develop convection tonight. If she fails to do this, her maximum winds will remain near 45mph until landfall. The ECMWF last night showed Beryl deepening to 997mb before landfall, supporting the idea that she can still strengthen slightly into a moderate tropical storm. Models are coming into tighter agreement on landfall right in the center of the window outlined yesterday, near Jacksonville, Florida plus or minus 30-40 miles or so. After moving inland, the blocking ridge that forced Beryl into the coast will break down in the face of a longwave trough moving across the northern U.S., and this should bring Beryl out to the northeast near the coastline of the Carolinas. If she makes it back over the water, redevelopment may be possible. Some models develop her into a stronger tropical cyclone as she moves out to sea than she ever was before landfall. The outer banks of North Carolina may have a blustery day if this occurs. For all of the southeastern states, this track will bring a few inches of rainfall to the drought-stricken areas that need it badly. It isn’t enough to bust the drought, but it’s rain.
Overall, Beryl is not a significant threat wind-wise, and will be more beneficial than not with her rainfall. A moderate tropical storm is expected at landfall, near 60mph in strength. This is a bit stronger than the NHC’s peak intensity forecast of 50mph. After Beryl, the Atlantic should be quiet for at least a couple of weeks, and significant activity may not return until the 2nd half of June due to an unfavorable pressure pattern over North America. Alberto and Beryl are not signs of an above-average season since they were not purely tropical developments, and 2012 should still come in at the end as a near-average season.
We shall see what happens!
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Once again we are watching off the SE U.S. coastline for subtropical or tropical development, this time from invest 94L which came out of the Caribbean, didn’t develop there, but now has a good chance of becoming tropical storm Beryl sometime tomorrow. I haven’t been able to post here on this yet, but if you follow my facebook page, earlier this week we discussed briefly the setup that could lead to this, as improbable as it is to have two storms like this develop in May. Once again we have an upper trough over the SE U.S. that is moving out over the water and will eventually stack up vertically with the surface low, lowering the wind shear and allowing warm-core transition. The models are in good agreement on at least some development occurring, with the exception of the GFS which may have initialization issues. As a deep trough digs into the western U.S., the same trough that is dragging Hurricane Bud towards Mexico, the deep-layer ridge currently over the southern Mississippi Valley will propagate northeastward and block 94L from escaping out to sea. The SW to NE orientation of this ridge will force 94L to turn back towards the southwest and likely make landfall in northern Florida or Georgia, a rare place to get a tropical cyclone landfall, but this is a setup that can make it happen.
This storm is different than Alberto in that it is of more true tropical origin, and it is much larger. For this reason, the models are picking up on it better than they did with Alberto. There is a large moisture shield associated with the system which 94L will be able to tap into for the next couple of days, and low-level moisture over the southeast U.S. is at a higher level than it was when Alberto formed. Subsidence from the big ridge in the south has made the mid-levels quite dry, and dry air entrainment will likely be a limiting factor in 94L’s development, but I think not as limiting as it was with Alberto. 94L will be moving over 27C waters in the Gulf Stream before making it to the coast, which should allow it to strengthen into a moderate tropical storm of around 60mph, the same peak as Alberto, but in reality a stronger storm because of its size and larger pool of moisture. SSTs do drop off a bit in the shallow coastal waters, and this combined with dry air entrainment may cause 94L to weaken just before landfall. A wildcard to consider is that landfall will be occurring in that very curved portion of the SE U.S. coastline, and such curvature can enhance convergence into the core of a tropical cyclone and help spin it up as it nears the coast.
Overall, 94L has a high chance of becoming tropical storm Beryl likely sometime tomorrow, and will be making landfall on the U.S. coast, likely somewhere between Daytona Beach and Savanna, GA. The landfall location will be pinned down better once the system has developed and starts moving towards the coast. This will be a decent rain event for Florida all the way up through the Carolinas, as the system will be turning northeast eventually as the blocking ridge moves out of the way. We may even have to watch for some redevelopment if the center gets back out over the water off of the Carolinas before moving ENE out to sea. In general this system should bring mostly good things to the SE U.S. in the form of drought relief, but tropical storm conditions will affect those near the landfall location.
After 94L, the Atlantic should be quiet for at least the next couple of weeks, as the pressure pattern over North America is becoming unfavorable to support low-level convergence in the early-season tropical breeding grounds, and we should see a lull in activity until the 2nd half of June. I will talk more about that later.
We shall see what happens!
Tropical Storm Alberto has formed off of the Carolina coast, fulfilling the concern we’ve had for a warm-core low to develop over the Gulf Stream beneath the upper-level trough split that has become cut-off near the SE U.S. coast. Alberto currently has tropical storm force winds of 45mph. Moderate convection has been sustained for about 18 hours now, mostly weighted in the northwest quadrant. The southeast quad is devoid of convection due to a lack of strong inflow and wind shear from the jetstream which is just to the south. Directly over the center of the storm, however, wind shear is weaker due to the elongated upper low becoming partially stacked with the surface low, something that some of the big-hitting models did not see happening a few days ago, but was still a concern based on some of their biases, which were discussed in the previous post. A stacked low has allowed convection to warm the mid-upper atmosphere and transition the low into a warm-core system that can now be considered a tropical cyclone. Upper-level anticyclonic outflow to the north of the system is further evidence of its warm-core transition.
Alberto will be meandering within weak steering currents off the SE U.S. coast for the next day or so before really going anywhere due to the blocking ridge over New England which is preventing any movement northward. Later tomorrow and Monday Alberto should begin moving northward or northeastward towards the North Carolina coast, likely giving it a close brush or a brief landfall around Monday before curving out to sea east of the mid-Atlantic coast. Given that most of the weather is weighted on the northwest side of the storm, residents along the North and South Carolina coasts should expect heavy showers and the possibility of tropical storm force winds even if the track keeps Alberto a bit offshore. Alberto is tiny, so the heaviest impacts may be localized to a rather small swath.
Alberto does have some problems to face over the next couple of days that will likely limit intensification. A low to the northeast and a new low forecasted to develop to the southeast coming up from the Bahamas will probably steal low-level inflow from the eastern side, making it difficult to develop thunderstorms there. The northern low moving towards the mid-Atlantic coast will also start shoving dry continental air down at Alberto’s northwestern side, which will likely start choking the system a bit, causing it to weaken when it begins moving northward. Sea surface temperatures are also only around 26C in Alberto’s section of the Gulf Stream, and drop off by several degrees close to the coastline. While this can support a tropical storm and even a minimal hurricane in this thermodynamic environment, the other conditions involved make me believe that Alberto likely can’t exceed a 60mph tropical storm, and a peak intensity between 50mph and 60mph is probable. Peak intensity should occur before any possible landfall, and Alberto will likely be weakening as it recurves.
Overall, Alberto is not a particularly significant or dangerous threat, but could bring tropical storm conditions to the North Carolina coastline as it brushes by or makes landfall there around Monday. This kind of situation was expected with this type of early-season setup, and the pattern delivered. After Alberto, the northwest Caribbean and the Gulf of Mexico will have to be watched for the next focus of disturbed weather later next week and beyond.
We shall see what happens!
Possible Hybrid Development off the Carolinas this weekend; West Caribbean Turns Wetter Along with Florida, Bahamas
The evolution of a complex pattern this week will create an opportunity for a hybrid low to develop off the SE U.S. coast, and at the very least a continued wet pattern from Cuba, Florida, and the Bahamas up to the Carolinas. An upper low moving across the southern U.S. over the next few days will be splitting off from the westerlies and becoming stuck near the SE U.S. coastline by Friday and into this weekend. An old frontal boundary has already stalled out east of Florida and extending down towards the Yucatan Peninsula, sparking showers across the entire area. This trough is tapping into a stream of tropical moisture originating in the eastern Pacific, where Tropical Storm Aletta recently formed and another monsoonal low is developing south of Mexico. As the upper low stalls this weekend, a hybrid, subtropical low may form underneath of it as it gets trapped south of a blocking ridge over New England for a few days.
The models are currently divided fairly evenly on their support for this event, with the UKMET and CMC leading the way and showing a tight low on their most recent runs, but the ECMWF and GFS are more timid with their solutions. The key difference seems to lie in the positioning of the upper low. The UKMET and CMC take the upper low closer to the coastline or out over the water, allowing the low shear environment to envelope the surface low and facilitate warm-core development. The ECMWF and GFS, on the other hand, keep the upper low inland and do not allow warm-core processes to intensify the surface low, though the ECMWF joins the UKMET and CMC in showing a weakening system as it moves inland, suggesting at least a partially warm-core low that would weaken over land. It will be interesting to see if the GFS is too far inland with the upper low because of an overdone forecast for tropical development in the western Caribbean, which would increase the resistance from the upper ridge southeast of Florida, thereby blocking the upper low from moving out over the Gulf Stream.
Despite the overbearing GFS, a festering low may start developing in the western Caribbean this weekend as well, and into next week may at least make the region look interesting after the southeast hybrid low has left the scene. With the MJO pulse currently reaching its maximum amplitude over the eastern Pacific and Caribbean, a system of interest cannot be ruled out, especially with the aforementioned classic early-season development pattern of low heights and old frontal boundaries south of the United States. This kind of a setup consisting of one threat to the north of the subtropical jetstream, and then a second threat to the south of the jetstream later, of more truly tropical origin, is a common progression of things in the pre-season or early hurricane season. We don’t always get development from either, but it sets up at least the opportunity.
Overall, at this time I don’t expect a particularly significant system to develop off the SE U.S. coast, however, the pattern favors some kind of mischief to take place as all of this tropical moisture made available by the MJO interacts with old surface troughs lying around in the region and the cut-off upper low that will be stalling nearby. Regardless, I expect the pattern will turn even wetter for the Carolinas this weekend as at least a surface trough laden with tropical moisture becomes blocked by the New England high and makes a move for the coast as it gets pulled underneath the upper low. Florida and the Bahamas may also get in on some more rain. Later next week, Florida and the Bahamas may get yet another shot of tropical rains as something gets drawn out of the western Caribbean, possibly a weak development threat.
We shall see what happens!
The time of year has come to start watching for our first tropical system to form in the Atlantic. The period from May 20th through June 5th is starting to look favorable for monsoonal activity to invade the western Caribbean and move north or northeast into the eastern Gulf of Mexico or the Bahamas. Convection should be enhanced in the area by a Madden-Julian Oscillation (MJO) pulse coming eastward into the eastern Pacific and western Caribbean in a couple of weeks. The model MJO forecasts below show the GFS being the most bullish, which is not surprising.
In fact, the GFS showed this happening 3 weeks ago. I don’t mean that it saw this event 3 weeks in advance. I mean that saw it happening way too early, and that is a model failing. Indeed, the GFS has been showing a tropical storm in the western Caribbean on almost every run for 3 weeks now in the western Caribbean, which until now has made no sense. However, it is worth mentioning now, because the pattern is more supportive for this to occur. A slower MJO progression as shown by the European models is called for, indicating that at some point during the May 20th-June 5th period we should see a pickup in tropical thunderstorm activity in the Caribbean that could lead to an early storm. This is this morning’s 12z GFS run’s depiction of the storm at Day 11, which may still be a bit too early:
Additionally, the upper pattern around this time is looking suspicious for tropical activity. The GFS ensembles have the polar jet retreating into southern Canada, with general ridging over the central and eastern United States. However, 500mb heights consistently sag south and east of the U.S., with a weak trough of some kind hanging back and reaching into the NW Caribbean, a pattern indicative of upward motion occurring in the tropics, and a trough becoming involved in the monsoonal circulation in the early season is a good way to get a quick tropical storm that gets drawn out of the Caribbean.
Now this is still nearly 2 weeks out, so details will be scarce until the time draws nearer, but if we do get some kind of a development, expect it to be drawn out of the western Caribbean northward into either the eastern Gulf of Mexico or across Cuba into Florida or the Bahamas, but likely being sheared to the east as it goes, typical of early-season systems. If anything the pattern should turn wet for these areas, hopefully bringing needed tropical rains to Florida. It is also possible that the eastern Pacific will see activity and possibly their first storm before the Atlantic has a chance to see any action. The time has come to start monitoring the tropics again.
We shall see what happens!