TropicalAnalystwx13's WunderBlog

Arlene moves into Mexico as a tropical storm; Watching for Bret

By: TropicalAnalystwx13, 4:30 PM GMT on June 30, 2011

Tropical Storm Arlene moved ashore this morning a little before 4AM CDT as a strengthening tropical storm with maximum sustained winds of 65 mph and a minimum central pressure of 993 mb. In Tampico, Mexico, winds in the order of 20-30 mph have been reported, with gusts higher than 35 mph. These winds are expected to get stronger as the day goes by and the city gets stuck under the right quadrant of Arlene's eyewall. At least 1-3 inches have already fallen in the city, and another 2-4" can be expected before Arlene moves into inland Mexico. This is likely to cause problems traveling, and mudslides/landslides will be a problem as well. Further north, in Brownsville, Texas, a little under an inch and a half of rain has fallen this morning as a result of Arlene's outer bands, and its possible that Brownsville could receive another 1-2" more, which is no undoubtedly helping the drought situation in that area. In addition to the heavy rains, wind gusts up to tropical depression strength have been reported within the heaviest rain bands. An earlier microwave pass of Arlene reveals that had the tropical system been over water another 6-12 hours, we would have probably seen our first hurricane. Because of the relatively flat terrain of the coast of Mexico, added to the cyclonic curvature of the Bay of Campeche, Arlene was able to really start to ramp up when it approached landfall earlier this morning. This same situation happened to Hurricane Alex of last year, which intensified from a strong Category 1 to a strong Category 2 hurricane between 2 NHC advisories.

Figure 1. Tropical Storm Arlene shortly after landfall south of Tampico, Mexico.

The intensity and track forecast for Arlene is not complicated, as the system should move westward into the mountainous terrain of inland Mexico. Since Arlene doesn't have an energy source anymore, it should rapidly weaken today, and likely dissipate before tonight is over. Some of the computer models are hinting at an area of low pressure developing south of the Baja of California in the Pacific later over the weekend, but it isn't a threat to develop at this time, with cooler Sea Surface temperatures.

Watching for Bret
Now that Arlene is out of the way, it is time to start watching for our second named storm, Bret. Typically, we do not see our first named storm until July 9th, and we do not receive our second named storm until August 1. So, we are ahead of schedule, and may stay ahead of schedule as I will type about later on in this post. Overall, the Atlantic is hostile, with 20-50 knots ruling most of the basin. There is a pattern of troughs and ridges across the Caribbean basin at this time. To sum it up, it is a pattern of high wind shear and low wind shear. As tropical waves pass through this area in the next couple of weeks, some will get caught under the troughs and likely not develop, but some could get caught under a ridge, just like Arlene did, which will provide a low shear environment, and allow for possible intensification. Sea Surface temperatures and Ocean Heat content are high enough to support a tropical cyclone, with much of the Caribbean running 2-4 °C above the 26 °C isotherm. In addition, several of the models are predicting a moderate to strong MJO signal by the end of the first week of July. This allows for a confluent area aloft, and enhances thunderstorm development, making it easier for a tropical cyclone to form. Considering that Arlene formed under a weak upward pulse, it will definitely need to be watched closely. None of the reliable computer models, such as the ECMWF and GFS, develop anything over the next week or so, but there have been hints by the majority of the models that there are going to be a couple of cold-core lows that form off the East Coast. While this isn't necessarily a threat, the lows will need to be watched in case one of them separates from a frontal boundary and becomes warm-core.

Figure 2. Current Wind shear across the Atlantic basin.

Next Update
I plan on taking a week or two off from posting, at least until the Atlantic basin starts to shift into high gear, since that is the basin I primarily cover. So, my next blog post will be between July 7-14.


Tropical Cyclones of 2011 Tropical Weather

Updated: 10:35 PM GMT on July 09, 2011


Tropical Storm Arlene develops in the Bay of Campeche but a threat to Mexico only

By: TropicalAnalystwx13, 12:49 PM GMT on June 29, 2011

[5:45 PM EDT update:]

Tropical Storm Arlene has risen in intensity his this morning, and is now at 60 mph, with a pressure down to 996 mb. The Mexican government has issued hurricane warnings, meaning that winds are exceeded to reach, or exceed, 74 mph within 36 hours. I personally believe that Arlene may reach hurricane status before landfall in the morning, but a 70 mph peak seems more likely at this point. Regardless, very heavy rains are expected to help end Mexico's drought. I will have a full blog entry regarding the latest update on what could be Hurricane Arlene and my July 2011 outlook for the Atlantic basin.

[End of update]

Arlene, the first tropical storm of the 2011 Atlantic hurricane season, is now upon us on this early Wednesday morning. Yesterday, hurricane hunters flew into what was previously Invest 95L, and found a well-defined center of circulation, a closed low pressure area, and maximum sustained winds of 40-45 mph. Thus, the National Hurricane Center upgraded this to a tropical storm. Current maximum sustained winds are thought to be around 40 mph, with a minimal central pressure of 1002 mb. However, given Arlene's satellite appearance, as well as measurable winds between 45-50 mph from an unscheduled recon flight, I believe Arlene is pushing 50 mph at this time. The main problem with the system yesterday was the lack of deep convection of the western side of the system, due to the presence of an upper trough in the western Gulf of Mexico bringing dry air and wind shear upon the system. Since then, wind shear has lowered, and dry air has dissipated, allowing for a favorable environment for strengthening. Arlene is currently moving to the WNW at a slow pace, between 5-10 mph. A turn to the west is expected later on today as the Texas/Mexico ridge and the ridge of high pressure in the Atlantic build back in across the Gulf states of the USA. Eventually, the system should bend back WSW before landfall in central Mexico tomorrow. Accordingly, the National Hurricane Center has placed tropical storm warnings for:


Figure 1. Surface Wind field and current TS warnings for Arlene made by the National Hurricane Center.

Intensity forecast
Due to Arlene's monsoonal origins, its take a while for systems like this to spin up. But once they do, they tend to strengthen rapidly. Fortunately for Mexico, Arlene only has about 24-36 hours before landfall, which will not give it much time to become anything more than a tropical storm. A hurricane is not out of the question at this time, since the cyclonically curved coast of the Bay of Campeche tends to spin up systems quickly, like Hermine and Karl of last year took advantage of. The official National Hurricane Center forecast has a peak of 60 mph. I agree that Arlene could peak here, but I would go a little higher, near 65-70 mph, on peak intensity given that it is probably pushing 45-50 mph at this time, and has all day to strengthen. The NHC is giving this system a 10% chance at hurricane status, but I think these chances are way higher, near 30%, especially if it takes advantage of the higher Ocean Heat values it is passing under, and it spins up quicker because of the topography of the Bay of Campeche. Regardless, as I have already mentioned, I forecast a peak of 65-70 mph. This may go up or down throughout the day, but I feel confident in 65-70 mph.

Figure 2. The National Hurricane Center's intensity forecast for tropical storm Arlene.

Track Forecast
There are not many things playing in Arlene's track forecast, making it relatively easy to forecast. As I wrote at the top of this blog, Arlene is currently moving WNW between 5-10 mph. However, a turn to the west is expected today as high pressure takes control of the USA, ruling out landfall there. If this system were able to strengthen more, it is possible a more northerly track could occur, but it would still be making landfall on northern Mexico. At this time, it is not expected to get terribly strong, so a landfall in central Mexico is a good bet. Before it makes landfall, as high pressure really begins to dominate, a turn to the WSW will occur, so residents in the Tampico area especially need to be prepared for tropical storm force winds and torrential downpours. The current National Hurricane Center track follows exactly what I just wrote above, taking it WNW to W to WSW up until landfall. The impacts to Mexico are expected to be just as they are to Tampico - flooding rains, strong winds, and even the possibility of landslides and mudslides. A total of 5-10" is being predicted in mainland Mexico, which will no doubt cause trouble just as Alex did to northern Mexico a year ago. I urge people to listen to their forecasting agency, or the National Hurricane Center, for updates on this system.

Figure 3. The National Hurricane Center's forecast track for tropical storm Arlene.

Next Update
My next update will be in the morning, probably before 10AM, with the current information on Arlene, along with current conditions in Mexico.


Tropical Cyclones of 2011 Tropical Weather

Updated: 11:51 PM GMT on May 14, 2012


Special Update: The first tropical storm of the 2011 Atlantic hurricane season forms

By: TropicalAnalystwx13, 12:31 AM GMT on June 29, 2011

As of the 8PM Special Advisory from the National Hurricane Center, we have Tropical Storm Arlene, the first tropical cyclone of the season. Since I have to go soon, I will not be doing a blog entry tonight. Instead, I should have one tomorrow mid-morning for sure. As of the 8PM advisory, maximum sustained winds are at 40 mph, and the minimum central pressure is 1003 mb. A peak of 60 mph is currently being expected by the National Hurricane Center, and accordingly, Tropical Storm Warnings have been issued for portions of Mexico.

Figure 1. 5-day NHC track forecast for Tropical Storm Arlene.

700 PM CDT TUE JUN 28 2011


LOCATION...21.2N 93.7W







Tropical Cyclones of 2011 Tropical Weather

Updated: 11:53 PM GMT on May 14, 2012


Caribbean disturbance could develop into a tropical cyclone; a threat to Mexico only

By: TropicalAnalystwx13, 11:10 PM GMT on June 26, 2011

Figure 1. Current visible satellite imagery of the Atlantic basin.

Well, the tropics are beginning to heat up now, something that we all knew would happen eventually. There is a tropical wave to the east of the Lesser Antilles, near 60W, that is producing a lot of disorganized shower and thunderstorm activity. No development of this wave is expected as it moves to the northwest, mainly because of moderate to high wind shear in the vicinity. One thing that really caught my eye, out in the Central Atlantic, is a tropical wave located near 35W. Convection associated with the system has not died out like it should have once it came off the African coast, since the waves that come off are cold-core. This, and the fact that an earlier ASCAT pass caught part of what could have been a decently defined circulation, makes me inclined to believe this is the strongest tropical wave so far this season. It will need to be watched closely over the next week or so as it moves east and enters the Caribbean. The main attraction in the Atlantic today though is an area of disturbed weather located just off the coast of the Yucatan/Yucatan peninsula. Visible satellite loops and surface observations, along with the 10M wind shift product, all reveal that a circulation is trying to develop with our disturbance. If this is the case, the system is trying to take advantage of the favorable conditions it has. However, it chose a very interesting place to start developing, as if it is not already on land, it will be tonight. Also, the system is a lot farther north than anybody could have, or I should say, did, anticipate. This helps to through confusion into the mess we currently have going on, because now the track of the system has to be readjusted, which ultimately means the intensity will need to be readjusted.

Into the Models
All of our reliable computer models, the ECMWF, GFS, CMC, and the NGP, dropped development of a system during the day yesterday. However, as of our latest runs, the ECMWF, CMC, and GFS all potentially develop at least a tropical depression. I believe the reason they dropped it yesterday is because of the fact that all of the models had the system tracking into the extreme southern part of the Bay of Campeche, thus limiting its time over water. As of this afternoons runs, the 12Z ECMWF foresees a weak to moderate tropical storm affecting the northern Mexican coast, in and/or north of Tampico, in 96 hours from now. The 18Z GFS doesn't really show much of nothing, potentially a tropical depression, but it shows the system being very broad. The 12Z CMC shows a tropical depression, which appears to be close to tropical storm strength (already has one closed isobar), moving into the Tampico, MX area in 54 hours. I didn't mention it above, but the 18Z NAM even develops an area of low pressure, possibly a tropical depression, and brings it into southern Texas and northern Mexico.

All in all, the models have, for the most part, jumped back on for development of this system.

Figure 3. 12Z ECMWF showing a weak/moderate Arlene making landfall near Tampico, MX in 96 hours.

Intensity/Track forecast
The intensity and track forecast will, as I mentioned above, have to be readjusted since this area of disturbed weather is located farther north than anticipated. The AOI is currently moving to the WNW at 10-15 mph, and if a surface circulation is indeed trying to develop over the Yucatan peninsula, it could be over water again by tomorrow morning. If this were to be the case, the chances of becoming a tropical depression/storm would definitely go up, because then it would have a good 48-96 hours over water. At this time, I believe that this area of interest will be tagged Invest 95L later tonight or tomorrow, and it should continue moving WNW. As the weakness between the Atlantic high and the Texas/Mexico high closes, this disturbance should begin to turn more to the west. My believe is that anywhere from Tampico, MX to just south of Brownsville, TX needs to watch this system, as they may receive tropical depression/tropical storm force winds and heavy rain by Wednesday-Friday of this coming week. As for intensity, I do believe this will eventually get classified as tropical depression #1, and ultimately tropical storm Arlene. However, it may not make it to tropical storm status until right at landfall, which would be fortunate for Mexico. Regardless of development, very rains are currently impacting the Yucatan, and should impact the northern Mexican coastline and inland Mexico by the end of the week. If Texas is lucky enough, it may even get some much-needed rain out of this. At this time, I give this system a 60% chance of ever becoming a tropical depression, and a 40% chance of ever becoming a tropical storm.


Tropical Cyclones of 2011 Tropical Weather

Updated: 11:54 PM GMT on May 14, 2012


Watching the SW Caribbean for mischrief; Another EPAC system possible

By: TropicalAnalystwx13, 10:23 PM GMT on June 24, 2011

The Atlantic basin as a whole is relatively quiet today - there is an area of thunderstorm activity in the western Gulf of Mexico, part of which is the remains of Beatriz's old vorticity maximum, and is attached to the tail-end of a frontal boundary. The threat for this to development is very minimal, and fairly nonexistent. But, this is a prime example of why things like this need to be watched, they can spin up fast and at anytime of the season, primarily early and late season. Elsewhere, the main focus of attention is an area of disturbed weather in the southwestern Caribbean. Most of the reliable computer models have shown development, but as of the latest run, 12Z, the ECMWF and NGP have dropped it. I believe they will show it come the next run however, the 12Z model run can be a bit screwy sometimes.

Into the Models
The 12Z GFS is farther south than any of its other runs, and a little weaker. By hour 48, or Sunday, the model is predicting a 1007 mb. low pressure area to move into the Yucatan, south of Belize. It then stalls the low pressure area just off the coast and deepens it to 1000 mb. before rising and crossing the coast, emerging in the Bay of Campeche by hour 96, next Tuesday. At hour 126, the GFS shows the low being forced south and dying over land. I personally believe that this particular solution being depicted by the GFS is not plausible, and unlikely at the moment. Next is the CMC. Unlike the GFS, the CMC model does not show any development before the Yucatan, and keeps it weak crossing it. The system emerges between hours 66-72, and the CMC makes it tropical storm Arlene by hour 96. At hour 108, Arlene, possibly nearing hurricane strength, makes landfall near Tampico, Mexico. As I aforementioned, both the ECMWF and NGP have dropped the development of the this system, at least for this particular model run. If we go back to the 0Z run, the ECMWF was showing at least an area of disturbed weather moving into the BOC, and the run before that had what looked like a tropical depression. The NGP's past run featured at least development into a tropical depression, but is interesting on this run, is that the model depicts a storm on the Eastern Pacific side to combine with the one on the Atlantic side over Central America. This I definitely do not see happening, although I do expect to see the ECMWF and NGP pick back up on development, especially once we can get a defined area of low pressure down in the southwestern Caribbean.

Figure 2. 12Z CMC @ 108 hours - Landfall near Tampico, MX.

Figure 3. 12Z GFS @ 126 - Landfall in the south-central Bay of Campeche.

My interpretation
I stated it in the first paragaph of this blog, but I'll repeat it - sometimes the 12Z model runs can be screwy, especially when we are talking about the GFS. For this reason, I am inclined to take these model runs with a grain of salt, and expect to see something more regular show up on the 18Z run. One thing I've noticed is that all the models are showing a farther south track, which keeps the system weaker than what it would be if it further north. My opinion is that the system will move quite a bit north of what the models are showing, emerging in the southern Gulf of Mexico, near 20/21 °N latitude. From there, it will move WNW/W before getting shunted south due to the replacement of a weakness in the eastern Gulf of Mexico by the Texas/Mexico ridge and the Atlantic ridge. A landfall near Tampico, MX, just as the CMC is indicated, seems most likely at this time, although that could change depending on how far south of north the AOI emerges in the BOC/southern Gulf of Mexico. Southern Texas is not out of the woods with this system yet, and they still need to monitor closely over the next couple of days.

Ocean Temps. & Heat Content
As you should know, one of the main reasons this season should not be as active as last is because of the Sea Surface Temperature difference. While we are still above average, we are below that of last years. The same thing can be applied for Tropical Cyclone Heat Potential, it is lower than last years. If we look at the image below, you can see that water temperatures are in the 28-30 °C range, 2-4 °C above what is needed to sustain a tropical cyclone. In the Caribbean, things are not much different; around 3 °C above what is needed to a tropical cyclone to thrive and develop. If we look at the Ocean Heat Content, most of the Caribbean and part of the Gulf of Mexico has enough TCHP to support rapid intensification. However, TCHP is significantly below what it was this time last year in the Caribbean, which is one of the reasons why I do not think we will see much out of our system before making it to the Yucatan. Additionally, once it crosses into the Gulf of Mexico, if it takes the track I am predicting, it will encounter very little Heat content, and cooler Sea Surface temperatures initially. So even if everything else was favorable, our system will not be in the best area to intensify into something more than a tropical storm.

Figure 4. Current Sea Surface temperatures as of 6/24/11.

Figure 5. Tropical Cyclone Heat Potential as of 6/24/11.

Wind Shear & Dry Air
Wind shear and dry air so far this season have been normal to below normal. In the Gulf of Mexico, wind shear values are right around the normal of 20-30 knots. However, in the Caribbean Sea, wind shear has risen to quite a bit above normal. This should change in the first week of July though as the Atlantic basin becomes prime for tropical development. In the dry air department, the Gulf of Mexico has been filled with it because of the extreme heat and sunshine that Texas has experienced so far this spring. But, in the Caribbean, that hasn't been a problem. When we add our Caribbean system into the mix, it seems that both of these will not be a problem. Wind shear in the southwestern Caribbean is moderate to high right now, yes, but an anti-cyclone is forecast to develop and move in tandem with the system as it progresses slowly WNW, lowering wind shear. With the system being so monsoonal in nature and so large, it is possible that it could rid a lot of the Gulf of Mexico of dry air, although it'd probably come back when the system moves out. In summary, our disturbance has favorable conditions, but it still has to struggle with two things, which I will talk about below.

Figure 6. Current wind shear across the Atlantic basin.

Figure 7. Current dry air across the Atlantic basin.

Land interaction & Competition
If you watch Levi32's tropical tidbit videos, you should know that he has talked about the set-up to be favorable for development. But, he has also talked about one of the two factors that may prevent our AOI from becoming a tropical cyclone - land interaction. As I mentioned above, there is currently a break between the Atlantic ridge of high pressure and the Texas/Mexico ridge of high pressure. This weakness should allow for our disturbance to gain a little bit of latitude before it closes off and high pressure dominates once again. Depending on how much latitude the disturbance gains, and where the low pressure area forms, land interaction may be a small problem or a large problem. At this point, it appears that land interaction between Honduras/Nicaragua and our system is inevitable, as our system is moving WNW, and does not have much time to gain latitude - the weakness will only be there for another 48 hours or so. If it does interact with these two locations, it may not get a chance to develop until after it enters the BOC/GOMEX. In that condition, it may not have a chance to become much more than a tropical depression. It should begin to interact with land in roughly 12-24 hours from now if it continued with its current speed.

One of the new problems for our disturbance that has arose is the potential for competition from the Eastern Pacific. There is an area of convection near 90W 10N that is showing signs of rotation, especially on visible satellite imagery. If this system further develops, it may not be a good thing if the Caribbean area wants to develop because it would steal all the convection and available energy. But, if the Caribbean system develops first, it would be vice-versa. It will be interesting see how this turns out nonetheless...Will the Atlantic get TD #1/Arlene? Or will the Eastern Pacific get their third named storm, Calvin?

Figure 8. Eastern Pacific system (left) and Atlantic system (right).


Tropical Cyclones of 2011 Tropical Weather

Updated: 11:55 PM GMT on May 14, 2012


Atlantic basin quiet

By: TropicalAnalystwx13, 11:17 PM GMT on June 13, 2011

The Atlantic basin is quiet and tropical cyclone free this evening with the downward phase of the MJO over our part of the world. There is a weak tropical wave to the east of the Lesser Antilles, with most of its convection separated near 50W 10N. This wave did have a well-defined inverted V signature during the day yesterday, but it appears to have weakened. As this wave moves to the northwest, it should enter an area of confluence aloft, or sinking air, which should suppress thunderstorm development. Additionally, there is a large amount of dry air and high wind shear in the eastern Caribbean, so no development is expected at this time.

Figure 1. Tropical Wave in the western East Atlantic.


Tropical Cyclones of 2011 Tropical Weather

Updated: 11:57 PM GMT on May 14, 2012


Hurricane Adrian on the decline in intensity

By: TropicalAnalystwx13, 1:50 PM GMT on June 11, 2011

After peaking as a 140 mph/946 mb. Category 4 hurricane, Adrian is on the rapid decline in intensity this morning. I will be the first to say, my forecast went horribly, horribly gone on guessing what Adrian would peak as. My forecast from two/three days ago called for a peak as a 115 mph Category 3 hurricane, because of very dry air to his north and northwest. However, when Adrian strengthened very quickly, he was able to build up his eye-wall to keep all dry air out. For a time on Thursday, I thought my forecast would come true. Dry air was getting into the eye-wall, and the northern part of it was being disrupted. However, Adrian forced the dry air out, built its eye-wall, and began strengthening once again. That is all in the past now, and we still have to focus on the storm, which is now only a borderline Category 1 hurricane, with 75 mph winds, and a minimum central pressure of 988 mb. Water Vapor satellite loops reveal that there is a large amount of dry air surrounding Adrian, which is pretty much evaporating the outer bands of the hurricane. Helping kill Adrian is sea surface temperatures, which were 30 °C the past few days. But now, Adrian is entering an area of cooler waters, barely 26 °C, which is what's needed to support tropical cyclones.

Forecast for Adrian
Given the hurricanes satellite appearance and unfavorable environment, Adrian is not going to last much longer. I'll give it to the next advisory to be a hurricane, but after that, weakening into a tropical storm is expected. With Adrian being an annular hurricane, I would have expected the storm to last longer, since annular hurricanes usually can sustain themselves longer in an unfavorable environment which would otherwise destroy a regular storm. CIMSS Tropical Cyclones show that wind shear is a moderate 10-20 knots, but is expected to increase as the storm heads west, then northwest. I will say though, it is impressive having a Category 4 hurricane for the "A" storm in the Pacific, the last this occurred was a decade ago, 2001's Hurricane Adolph, which reached 145 mph. The last time a major hurricane was recorded as an "A" storm in the Pacific, was just a year later, with 2002's Hurricane Alma. Here is my forecast for Adrian in 12-hr intervals:

Current: 75 mph/988 mb.
12-hr: 50 mph/TS
24-hr: 35 mph/TD
36-hr: Remnant Low
48-hr: Dissipated


Tropical Cyclones of 2011 Tropical Weather

Updated: 11:58 PM GMT on May 14, 2012


Enter Adrian! The first cyclone of the 2011 Pacific hurricane season forms!

By: TropicalAnalystwx13, 2:31 PM GMT on June 08, 2011

The first tropical storm of the 2011 Pacific hurricane season has arrived, forming last night a couple hundred miles south of Acapulco, Mexico from the previous Tropical Depression #One-E. Adrian, currently a 70 mph/994 mb. tropical storm, is forecast to become the Pacific's first hurricane later on tonight by the National Hurricane Center, but by the way the storm is organizing, I believe we will have Hurricane Adrian this afternoon. CIMSS Tropical Cyclones analysis reveals that wind shear is a low 5-10 knots, down from the moderate 10-15 knots it was experiencing yesterday. Visible satellite loops show outstanding outflow on the western side of the system, and very well-defined banding features wrapping around in the system, almost completely around the center of circulation. Both of these are indicators that Adrian is quickly approaching hurricane status. The system is moving to the northwest at approximately 5 mph, under sea surface temperatures 1-3 °C above normal. This, combined with the low wind shear, may be enough to allow for rapid intensification, which the SHIPS is giving a high probability to. If this were to occur, it is very possible that Adrian would become a major hurricane, with winds over 111 mph.

Figure 1. Visible satellite imagery of TS Adrian.

Intensity forecast
My forecast for Adrian calls for gradual strengthening throughout much of today, reaching hurricane status later on this afternoon. From there, I expect that rapid intensification will commence for nearly 24 hours, and Adrian will be a Category 2 hurricane by tomorrow afternoon. It may be able to strengthen for another 12-24 hours or so before it begins to enter an unfavorable environment, with high wind shear and lots of dry air. Once it enters this area, I expect the storm to begin the weaken, and it will likely be a tropical storm again by next Monday. However, if Adrian strengthens more than expected, the storm will last longer since it will be able to hold off the unfavorable conditions for a while. Here is my forecast for Adrian in 12-hr/24-hr intervals:

Current: 70 mph/994 mb.
12-hr: 75 mph/Category 1
24-hr: 95 mph/Category 2
36-hr: 110 mph/Category 2
48-hr: 115 mph/Category 3 *MAJOR*
72-hr: 115 mph/Category 3 *MAJOR*
96-hr: 95 mph/Category 2
120-hr: 75 mph/Category 1

Track forecast
Tropical Storm Adrian is not expected to be a threat to any landmasses, as it should head northwest, paralleling the Mexican coastline, before eventually dying out later on next week. Tropical Storm Watches have been posted for portions of Mexico (see image below), but it is not climatically favored for systems to make landfall on the Mexican coast, like we saw last year, where most storms went out to sea without having any impacts on Mexico besides wave action. This is the National Hurricane Center's 5-day track forecast for Adrian. As you can see, no landfall is expected.

Figure 2. NHC's 5-day track forecast for Adrian.

Figure 3. Watches/Warnings map for Adrian.

Extended forecast for Atlantic
Invest 94L was deactivated this morning, and is no threat to develop anymore. There is a slight chance that the remnants could bring drought-stricken Florida some much needed rainfall, but I wouldn't particularly bet on it. So now that 94L is gone, what else is there to track? Well...the Atlantic basin has no other areas of concern to watch for development, so we are free for at least the next 10 days or so, as the downward, dry phase of the MJO moves strongly into our basin. However, as we head into the last week of June or so, the upward phase of the MJO is forecast to move back in, which may allow for development in a situation similar to 94L's. What will be different this time around though, is that not only will it be climatically favored, it would have the upward phase of the MJO going for it, low wind shear, no dry air, etc. Basically, whatever may try to develop down in the western Caribbean or Gulf of Mexico later this month will have a much better chance than what 94L did. This is when I believe we will see Arlene.

Figure 4. The MJO forecast showing the incoming downward phase across the Atlantic.


Tropical Cyclones of 2011 Tropical Weather

Updated: 11:59 PM GMT on May 14, 2012


Tropical Depression One-E forms in the Pacific; 94L unlikely to develop

By: TropicalAnalystwx13, 8:05 PM GMT on June 07, 2011

The first tropical depression of the 2011 Pacific hurricane season has developed, according to the 8 AM PDT advisory from the National Hurricane Center. Maximum sustained winds are currently at 30 mph, with a minimum pressure of 1006 mb. The official forecast calls for TD #1 to move very slowly to the northwest, with gradual intensification. Ultimately, the NHC is forecasting intensification into an upper-end Category 1 hurricane by the weekend, with a gradual decline in strength thereafter, likely due to strong Wind Shear. No watches or warnings have been issued yet, probably because the threat to land is fairly minimal. Visible satellite loops show well-defined banding features, and nice inflow coming into the center of circulation. Water Vapor satellite loops reveal that TD #1 is in a fairly dry environment, but this should not hinder development too much. Lastly, CIMSS Tropical Cyclones analysis reveals that Wind Shear is a moderate 15-20 knots, but an anticyclone is situated close to the southeast, which will prevent the shear from increasing.

Figure 1. RGB satellite imagery of TD #1 in the Eastern pacific.

Forecast for TD #1
My forecast for TD #1 is very similar to the National Hurricane Center's, with gradual intensification, along with slow movement to the northwest. I do see this system becoming an 80-90 mph Category 1 hurricane before it begins to weaken, with the possibility of a slightly higher storm, depending on how fast it intensifies over the next few days. Sea Surface temperatures are approximately 30 °C, well above the threshold for a tropical system to be able to sustain itself. I do not see TD #1/soon-to-be-Adrian being a threat to land, and if it is, only some light rain or cloud cover will occur. Here is my forecast for the system in 24-hour intervals:

Current: 30 mph/1006 mb.
24 hr: 45 mph
48 hr: 70 mph
72 hr: 85 mph
120 hr: 75 mph

(I expect TD #1 to reach peak strength between hours 72 and 120, at 90 mph.)

94L no threat to develop
After putting up a valiant fight, it appears that it is time to discount 94L as the first tropical depression of the 2011 Atlantic hurricane season. After several days of very favorable conditions, Wind shear is on the increase, and its chances of development into a tropical cyclone are near 0%. Heavy rains are still a concern for Cuba, Jamaica, Grand Cayman, Haiti, and the Dominican Republic however. The forecast for this Invest is for it to move very slowly to the N, or possible the NNW, before entering the eastern Gulf of Mexico. Needless to say, development is not expected in this area either, with high Wind shear. It is possible that this system could bring some much-needed rain to the drought-stricken state of Florida by the weekend. But we can only hope and pray. This is the last time I will mention 94L.

Figure 2. Visible satellite imagery of Invest 94L.


Tropical Cyclones of 2011 Tropical Weather

Updated: 12:00 AM GMT on May 15, 2012


2011 Atlantic hurricane season predictions; Tropical Weather Outlook

By: TropicalAnalystwx13, 10:27 PM GMT on June 01, 2011

Today marks the first official day of the 2011 Atlantic hurricane season, which is forecast to be a very busy one according to many popular forecasting agents such as Colorado State University (CSU), Tropical Storm Risk (TSR), and the National Hurricane Center (NHC). I am predicting an above-average hurricane season, with an 85% chance of this season being more active than normal, a 10% chance of this season being normal, and only a 5% chance of this season having less activity than the climatological mean of 1995-2010. I am predicting that the Atlantic basin will experience 15-18 named storms, 8-12 hurricanes, and 4-7 major hurricanes, 1-3 of these becoming the major Category 5 hurricanes.

There are several factors that go into this such as Sea Surface temperatures across the Atlantic basin as a whole. They are running 1-2 °C above average in most areas, which is more than enough to support tropical development at any given time. Another important factor that ties in with temperatures in the Atlantic is Ocean Heat Content (OHC). This is the amount of energy stored in the water. This can allow for rapid and explosive intensification. Values in the Caribbean at this time are not quite warm enough to support rapid development, but it is getting close. As we approach the peak of the season, we can expect to see these values soar.

More important factors include wind shear, dry air, and ENSO. Because we are so early in the season, the Subtropical Jet Stream is created high wind shear over a lot of the Atlantic right now, with the exception of the Gulf of Mexico. However, the Subtropical Jet Stream is slowly retreating north, and wind shear will begin to lower, especially in the Caribbean and off the East Coast of the United States. Dry Air is not really a problem across the Atlantic basin right now, but there is quite a bit in the Gulf of Mexico. This should reduce over the next couple of weeks as the basin becomes moister.

As for ENSO, or the El Niño-Southern Oscillation, there are three categories: El Niño, Neutral, and La Niña. In an El Niño season, the Pacific is more likely to see an above average season because high wind shear and cool Sea Surface temperatures limit the number of tropical cyclones in the Atlantic basin. An example of this would be the 2009 season, which was well below average. In a La Niña season, the Atlantic is more likely to see the above average season, because there is low wind shear and warm Sea Surface temperatures. An example of this would be last year (2010), when we had 19 named storms, 12 hurricanes, and 5 major hurricanes.

Unlike last year, I am forecasting several impacts to the continental USA. This is because the Bermuda High is expected to be set-up differently than it was last hurricane season, a set-up that favors systems to hit the USA. Some of my analogue years are: 1951, 1989, 1996, and 2008. All these years featured several tropical cyclone landfalls on the USA, and the pattern matched what it is expected to look like this year. The two key areas of concern I am particularly worried about is the coastline of Texas, and the coasts of both North Carolina and South Carolina. In most of these seasons, a tropical cyclone made landfall on one or both of these areas. Everyone living along the coast of the USA needs to be prepared, but these two areas in general need to really pay attention to what is occurring in the tropics and be prepared if a system develops and heads your way.

This concludes my 2011 Atlantic hurricane season forecast. I’d appreciate comments and/or concerns about this forecast!

Invest 93L a threat to develop
A surprise disturbance became very organized yesterday afternoon and evening from the leftovers of the MCV that traversed the Midwest and Northeast earlier this week. Deep convection developed yesterday while the system as situated off the coast of North Carolina, and an ASCAT pass revealed an elongated, but rather organized, circulation, so the National Hurricane Center designated it Invest 93L. As it moved southwest, it gathered organization, and strengthened a little. The invest moved ashore the eastern coast of Florida earlier this morning, but it appears that it has now entered the Gulf of Mexico.

Figure 1. Visible satellite loop of 93L crossing Florida.

Forecast for 93L
Wind Shear in the eastern Gulf of Mexico is a light 5-10 knots, which is conducive for development. There is quite a bit of dry air surrounding 93L, but that is just about the only thing going against the development of this system besides its speed. My forecast calls for intensification through tonight and into tomorrow, with the potential for a tropical depression by tomorrow night. The hurricane hunters are scheduled to fly into Invest 93L to determine whether or this becomes our first depression of the season. I do see the potential for it to become a weak tropical storm being making landfall on the coastline of Texas sometime on Thursday. This is not expected to be anything major, but something interesting to say the least. I am currently giving this system a 40% chance for development within the next 48 hours.

Caribbean disturbance organizing

Shower and Thunderstorm activity continue to increase in the southwestern Caribbean with our disturbance, which appears to becoming more organized. This is likely because of the decreasing shear atop our pre-invest 94L, which is down to 20-40 knots. And shear is expected to continue to decrease, which will help for further development, especially starting tonight and tomorrow.

Figure 2. AVN Satellite of the Western Atlantic, including 93L and pre-94L.

Forecast for pre-94L
I expect our disturbance to be tagged Invest 94L either tonight, or tomorrow. By tomorrow afternoon, I expect this system to look a lot more organized than it ever has, thanks to more favorable conditions. I expect pre-94L to meander in its general vicinity through the rest of this week, before potentially moving NW towards the Gulf of Mexico. I am currently giving this system a 20% chance of development within the next 48 hours.


Tropical Cyclones of 2011 Tropical Weather

Updated: 12:01 AM GMT on May 15, 2012


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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