Wxchaser97's Tropical Weather Blog

Tropical Storm Dorian forms, long range threat to Caribbean and possibly US

By: wxchaser97, 2:24 AM GMT on July 25, 2013

Tropical Storm Dorian
The fourth named storm of the 2013 Atlantic hurricane season formed earlier this morning. The named storm is the second farthest east forming named storm in July, only eclipsed by Hurricane Bertha from 2008. Dorian formed from a strong tropical wave that came off of Africa a few days ago. After gaining a well-defined surface low and persistent convection, the invest became a tropical depression in the early morning hours. Later this morning, an ASCAT pass along with satellite derived intensities showed that TD-4 had intensified into TS Dorian. Dorian continues to fire organized convection with a inner core trying to develop and banding features present. Also anticyclonic outflow is becoming better defined as shear is pretty low over Dorian. However, the convection isn't as deep as earlier since Dorian is being affected by cooler waters/stabler air, but it's still holding on. The current storm info and satellite image can be found below.

5:00 PM EDT Wed Jul 24
Location: 14.6°N 31.4°W
Moving: WNW at 20 mph
Min pressure: 1002 mb
Max sustained: 50 mph

Forecast for Dorian
The environment out ahead won't be perfect for strengthening in the short-term or the long term. For the next day or so, the SST's will be the biggest hurdle for Dorian. The ocean temperatures where Dorian is at are around 25C, which isn't favorable for development. There isn't as much energy in the water to be able to sustain deep convection. However, wind shear is low and Dorian has a nice moister bubble. SHIPS analysis has shear less than 10kts for the next 2 days with 700-500mb RH values near 70%. This is allowing Dorian to keep itself alive over the cooler waters, even organize its structure a little. These conditions should persist over the next 1-2 days as Dorian heads WNW. Dorian should be able to maintain its intensity or even strengthen a little even though SST's are marginal at best. It is looking way less likely that Dorian dies, or even weaknes much, from the cool waters. As Dorian gets farther west the SST's will warm again to more favorable levels. This means there will be more energy for thunderstorm to grow and sustain themselves as ocean heat content will also be on the rise. However, Dorian will be moving into an area of dry air and possibly shear in the longer run. While the models are showing the upper air patterns to be less hostile than in earlier runs, Dorian may still have to contend with some moderate shear. An upper level trough over the central ATL impact Dorian with some shear, especially if he gets farther north. Even if Dorian experiences some shear, I don't think that will be the end of Dorian considering that it is already doing well and the shear wouldn't be super strong. Dry air will also be a factor in how strong Dorian gets. While Dorian is in a moist environment right now, it will be moving into dry air over the next few days. As stated earlier, Dorian has a nice moister envelope and this should help it from the ill effects of dry air. I am worried that dry air may still be able to penetrate Dorian and disturb its core some, which would slow intensification. However, I don't think the dry air or shear would be fatal or even critically harmful to Dorian as the warm SST's should offset some of the ill effects. With all of this in mind, I am advertising a slowly strengthening tropical storm over the next 5 days, especially toward the end of the forecast period. There is a small chance that Dorian makes a run at hurricane status near the Lesser Antilles, but at this time I think Dorian will remain a TS. After passing the longitude of the Lesser Antilles, it is anyone's guess as to how strong Dorian gets. Dorian should be in a favorable environment for intensifying, but due to uncertainty in the long term pattern and track, I'm not going to make much of a guess. My intensity forecast is somewhere in the middle of the intensity model guidance, but they are all spread out.

The track forecast for Dorian is a little more clear cut in the shorter term, but very uncertain in the long term. Right now, Dorian is still heading mostly WNW, though it may be making a wobble to the W a little. The general WNW heading should continue for the next couple days as it still feels the weakness to the northwest. CIMSS steering maps show the WNW heading pretty well. As Dorian gets farther west, the ridge to its north should strengthen and expand farther west. This ridge is expected to become very strong, 600dm at 500mb, and it is expected to close off the weakness. The southern ridge axis is also expected to follow Dorian for a time, keeping Dorian on a westward heading in a few days. The statistical, dynamical, and global models are in pretty good agreement on where Dorian goes over the next 5 days, regardless of intensity. My track forecast is just a blend of the models and is similar to the NHC track. The models diverge after about day 5 or 6 on where Dorian will go. They disagree on whether a trough to the north will be able to recurve Dorian out to sea, into the US, or not affect Dorian much. Timing is key to the whole long range track forecast. If the trough is slower than expected, then Dorian will go farther west, and the same if the ridge extends farther west then expected. If the trough comes in stronger or the ridge moves west/strengthens slower, then Dorian has a greater chance of being pulled out to sea. Also the intensity of Dorian will be a factor into where it goes as a deeper system will feel the upper level steering pattern more than a shallow system. Right now, the track after the longitude of the Lesser Antilles is all just speculation. Everybody in the northern Antilles, the Bahamas, the entire East Coast, and parts of SE Canada need to be paying attention to the evolution of Dorian.

Tropical storm Dorian is the second storm to form in July this year, with the other being TS Chantal. Both formed from strong tropical waves in the deep tropics. This is a sign that conditions are already getting favorable for Cape Verde development and it is only late July. As conditions improve even more in the next month, we could be looking at an active Cape Verde season in the ASO period. Whether an East Coast troughing pattern or riding pattern will take hold remains to be seen so everybody needs to be reviewing their hurricane plans. Also, a storm that forms closer to home will have a greater chance of impacting the US regardless of the pattern.

Forecast Intensities

INIT 25/0200Z 45 KT 50 MPH
12H 25/1200Z 45 KT 50 MPH
24H 26/0000Z 45 KT 50 MPH
36H 26/1200Z 45 KT 50 MPH
48H 27/0000Z 45 KT 50 MPH
72H 28/0000Z 50 KT 60 MPH
96H 29/0000Z 50 KT 60 MPH
120H 30/0000Z 60 KT 70 MPH

Forecast Track

Watches, Warnings, and Advisories


Have a great night everyone. I'll be adding my graphical track forecast, along with a section on 99L, in the next hour. I am releasing my blog now so it is out before the 11pm advisory. I'll do a new update sometime tomorrow afternoon or night.


Invest 98L a threat to develop, future is uncertain

By: wxchaser97, 5:02 AM GMT on July 24, 2013

A surface low has formed in conjunction with a tropical wave about 150 miles southwest of the Cape Verde Islands. What started out as another robust tropical wave over Africa has been able to organize over the east Atlantic into a developing tropical cyclone. Recent ASCAT passes, satellite, and microwave imagery show a well-defined, closed low-level center. While the intensity and persistence of convection has been an issue for a while, convective patterns have been organizing. With convection beginning to burst over the center, development into a TD or TS is likely. There is even some banding trying to get its act together. The current storm info and satellite image can be found below.

AL, 98, 2013072400, , BEST, 0, 133N, 256W, 25, 1008, LO, 34, NEQ, 0, 0, 0, 0, 1013, 150, 40, 0, 0, L, 0, , 0, 0, INVEST, M,

As mentioned above, 98L is probably already a tropical depression. ASCAT shows a closed circulation with 30kt wind barbs and convection is persisting over the center. The warm waters off the African coast and tolerable amounts of wind shear have allowed 98L to get a closed surface low and some convection. The only reason as to why 98L wasn't classified as a depression at 11pm last night was because they are waiting for persistence of convection over the center. Since the convection looks like it wants to persist, I expect that we should have a TD or weak TS at 5am.

Invest 98L only has about another 24hrs or so of favorable conditions before the SST's drop off. Wind shear is expected to stay relatively light for the next several days, as predicted by the GFS and the SHIPS. Dry air/SAL shouldn't be much of a hindrance as 98L has a large moister bubble protecting it from dry air intrusion. This is something to watch to see if it holds up over the next few days, but it still looks like dry air won't be the main problem. Also, the trade winds aren't going to be as strong as they were with Chantal, which means a slower speed for 98L. Chantal was the TS that developed in the Central Atlantic from another strong tropical wave last week. It suffered a painful demise from strong trades and strong shear, something 98L shouldn't deal with. So for the next couple days, the main issue for 98L will be the cooler SST's. My intensity forecast, though not in my usual format, calls for a TD/weak TS forming later today with little to no strengthening afterward for a couple days. Once it gets farther west, it should move back over warm SST's and more substantial strengthening can occur. The environment should remain relatively favorable for the rest of the forecast period, it approaching the Lesser Antilles. This won't be a major hurricane, or likely not even a hurricane, knocking down on the Lesser Antilles, but a moderate to possibly strong TS seems good. I don't see 98L degenerating over the SST cool pocket since other factors are still favorable, but it is still something to keep in mind.

98L had been moving almost due west over the past couple days as it slowly moved off the African coast. The invest has just now started to feel the weakness to its northwest and thus has turned to the west-northwest. The current position of 98L is much farther south than what the models were showing just a couple days ago. They were taking it WNW to NW right off the bat into less favorable conditions, but 98L has been moving along with the flow. Since 98L is farther south than what the models were dictating, it should be over the cool pocket for a little less time than thought. This is another plus for it surviving. The weakness out ahead of the invest is not a terribly strong one, but it is enough to cause 98L to gain some attitude of latitude. This should cause 98L to gain several degrees in latitude as it treks to the WNW over the next couple days. Once we get past a few days in time, the more westward motion should begin to take hold again. The ridge of the Atlantic is supposed to get stronger and build back to south/west. This will cut 98L away from any trough to its north and probably stop the northward component. Timing is key to the track of this invest. If it were to move faster than expected, then it would be able to outpace the high building back in and have a greater chance of riding the edge of the ridge out to sea. Right now, 98L should move slow enough that the axis of the high keeps 98L moving toward the W-WNW. This is supported by the statistical, dynamical, and some of the global models. The ECMWF and UKMET, however, bring 98L out to sea. It should be noted that they have been faster/farther north with 98L for some time and I don't buy into that solution, but it should still be monitored just in case. Invest 98L should be near the northern Lesser Antilles in about 5 days, likely as a tropical storm. My track forecast is right in line with the dynamical and statistical suite. I'll be doing my full track and intensity forecast/graphic when we have a tropical cyclone.

Chance of development in the next 48hrs: 90%

Have a great night/morning and I'll have a new blog update on 98L later today.

Tropical Atlantic Hurricane

Updated: 5:09 AM GMT on July 24, 2013


Rest of July should be relatively quiet, season gets active afterward

By: wxchaser97, 8:43 AM GMT on July 14, 2013

It's been a while since I've done my last blog, about two weeks. I was first on vacation and then had internet issues that prevented me from doing a blog update. While I was offline, I missed the second half of Hurricane Dalila, all of Hurricane Erick, invest 94L in the Atlantic, and TS Chantal. Chantal's remnants have been giving Hispaniola, Cuba, the Bahamas, and the SE US stormy conditions, but are no threat to develop. I know, I've missed a decent amount of activity. I may do a review blog for the Pacific and/or Atlantic activity I missed over the next day or two. Until then, lets touch on the rest of July and beyond. The first half of July has featured a few pretty strong African Easterly Waves (AEW's), including one that developed into a TS in the deep tropics. July isn't a favorable time for the development of storms from these waves out in this part of the Atlantic. This is because of the outbreaks of SAL and the stronger trade winds. Chantal was pushed very fast, at a record speed actually, by the trades. This, along with the Caribbean low-level jet, caused Chantal to have trouble closing off a circulation. This will be a problem for future waves until the high retrogrades farther north weakening the trades in the MDR and Caribbean, along with the Cllj weakening. This should give waves a higher chance of developing as they can actually close and strengthen a circulation without issues. However, more favorable conditions in that regard will come more around very late July and the beginning of August. As mentioned earlier, the Saharan Air Layer (SAL) and dry air have been causing issues development wise for waves in the MDR and E Caribbean. Since we are getting stronger waves more frequently, and the ITCZ is slowly moving farther north, the SAL outbreaks are just starting to get reduced in frequency and strength. This would mean that there won't be as much dust and dry air in the environment that would hamper the formation of convection. Conditions should only improve in this regard as we head into August. However, the Atlantic is in a downward phase in the MJO. This means there is sinking air in the Atlantic which suppresses convection. For the time being, as long as we stay in the downward phase, waves will have a harder time developing. This should stay about the same until we get into August, more on that later. The final thing to touch on is the SST profile. With the farther south A/B high, this has increased the trade winds in the MDR and Caribbean. This has caused the SST anomalies to come down some. However, the MDR still remains above average in regards to the SST anomalies and relative to the global tropics, meaning a favorable SST profile. Should see waters warm as the trades weaken, which is normal. What you're probably wondering is what this all means for the rest of July. Well, it means that while we can't rule out development, it is unlikely that we get a storm in the MDR. As for something close to home, it is always possible to get a quick spin-up somewhere. In-fact, there is a few areas that are, barely, being watched for development. One is an ULL near Bermuda, another is from a decaying front over the GOM, and a tropical wave in the NW Caribbean. All of these have low chances, <20%, of ever developing. The ULL will probably go over land or run into unfavorable conditions, the low in the gulf has unfavorable conditions and very little time to develop, and the t-wave has no model support. I personally think that none will develop, and the NHC doesn't have any of the areas highlighted. While they likely won't develop, they will bring some rain and wind to the areas they impact. Other than these low threat systems, there is nothing on the models regarding home-grown development or are there indications of any happening. Now is the time to make sure you have all of your hurricane supplies ready, an emergency kit prepared, and be always knowledgeable and ready for something to happen, as the next couple months will be active.

I have posted a few images regarding the 2013 Atlantic season. First, the tracks of all the invests and storms to form this year. It shows 3 storms, which is above normal for this time of year, and one that came out of the deep tropics. It should be noted that invest 92L was likely a tropical depression, maybe a weak TS, in June in the MDR. The next image is a MJO plot. It shows the MJO from the last month, plus MJO forecasts from some models. The circle in the middle of the plot is where the amplitude of the pulse is low, a "cone of silence" of sorts( I know the term is for radar, but you know what I'm getting at). The MJO is barely in this circle right now, and will take its time to get out. The final image is the global SST anomaly image. It shows a negative to neutral PDO, a cool neutral ENSO state, a near normal Caribbean, below normal GOM, above normal C/E ATL, a cool Gulf of Guinea, and a positive Atlantic tripole(while the signature is less pronounced than in previous months, it's still there).

Alright, now is time to talk about August and beyond. This is where I, and other people, expect the heart of the 2013 hurricane season to really get going. First, I'll touch on potential tracks of the storms. This year, the Bermuda high is pretty strong and dominates the sub-tropical Atlantic. Unlike recent years, there is persistent ridging over the east coast, instead of troughing. This means there is now weakness to pull most of the storms out-to-sea before impacting land. Now, the weakness is over the US, along with the stronger, more expansive ridge, would cause a heightened risk for US landfalls. Also, instead of this being a Mid-Atlantic/Northeast year, I am expecting a Southeast/GOM year in terms of landfalling storms. I'm not trying to doomcast or anything, but the pattern supports multiple landfalling tropical cyclones in the US. We have seen this type of a pattern since 2008 and farther back, and we all know what happened in the 2000's. Of course, the million-dollar question is: Will the favorable pattern for landfalls remain in place? I think it will, but this is the weather we're talking about, and it could change. The models continue to show the high remaining dominate and expansive and people should be ready for an Active year landfall wise. I also think the time is up for our major hurricane landfall drought. The last official US major hurricane landfall was Wilma from '05, but a few storms (Ike, Sandy, etc) were pretty much major hurricanes at landfall. With the pattern 2013 is in right now, I feel it is pretty likely, roughly 60%, that it ends and 40% that it doesn't.

Now that we got the potential tracks taken care of, we can talk about the strength of the storms and the factors for development. As we get into August, conditions should get more favorable for development out in the MDR. Trade winds should weaken, SST's should warm more, the AEW's will remain strong/get stronger, and the MJO will be going into a more positive phase in our part of the world. If the MJO is in its upward phase, then there is more upward motion, lift, and moister in the Atlantic, promoting convection and further development of waves. Like mentioned earlier, with the trades weakening, along with the cllj weakening, waves should be able to develop as they can actually close off a circulation. This weakening of the trades should begin in the coming weeks, as climatology dictates, as the high moves farther north. As noted earlier, the MDR is running AOA normal. This means there is a good amount of fuel for developing storms. While the Caribbean is slightly below normal to normal, there is plenty of ocean heat content. So there is warm water below the surface, and it won't take long for the Caribbean to rebound as well. As the SST's have been doing pretty good anomaly wise, vertical instability is around normal instead of being far below normal. Storms have more energy available in the atmosphere to build deeper convection, thus having stronger storms. This was a problem the past couple seasons and we weren't getting as strong of storms in the deep tropics. Wind shear has been running AOB normal, and should remain that way, which will allow storms to keep a well-defined circulation and convection over the center. All of the factors are coming together for an active few months ahead. However, some of the computer models are seeing otherwise. The ECMWF is seeing above average pressures over the basin which is unfavorable for development. It has also shown El Nino developing. Both the unfavorable MLSP and El Nino are unlikely as we have had lower pressures for most of the time and neutral ENSO conditions with no intentions of changing. The CFS has flip-flopped between unfavorable conditions and favorable conditions in the Atlantic, and the UKMET has been advertising a less-active Atlantic as well. I'm not buying into those solutions of an inactive season as the models are having a hard time resolving the neutral ENSO state, and our already relatively favorable environment. My seasonal prediction is pretty well inline with the major prediction centers and the average of the wunderground members. My range is now 15-19 storms, 7-10 hurricanes, and 2-5 majors. My direct numbers are 18-9-4, but we will probably end up a named storm or two less. I am sticking with 18-9-4 for the heck of it, even though we will probably end up with 16 or so storms, but I still believe the hurricane /major numbers will verify. The Atlantic is getting ready to get pretty active, and all we can do is strap in for the ride.

Have a great night and morning and I'll probably do a review blog or two today or tomorrow. If I don't, then my next update will be when the next real threat for development in the Epac or ATL arises.


TS Dalila forms, still a threat to Mexico

By: wxchaser97, 7:31 AM GMT on July 01, 2013

TS Dalila
TS Dalila has had its ups and downs over the past day. Right after my blog update last night, she was doing pretty well. It had deep convection over the center with a few curved bands feeding into the storm. Satellite estimates were rising and it looked like we had a strengthening storm. Then, as the morning went on, Dalila began to become less organized. There wasn't as much deep convection over the center, it lost some of its bands, and the center became a little less defined. What caused Dalila to become less organized is kind of a mystery. Some argue that mid-level dry air caused convection to wane, but precipitable water maps, water vapor imagery, and SHIPS analysis show that this was likely not an issue. The only thing that I can really think of to cause the issues is some southerly shear. The NHC noted this in previous forecast advisories as well. However, over the past several hours, Dalila has been able to get back to an organization trend. An eyewall/inner core is trying to develop and deep convection is starting to develop over the center again. This is likely a result of shear decreasing a little in the vicinity of Dalila. TAFB and UW-CIMSS ADT are at 3.0 and 3.1 respectively with SAB coming in at 2.5, all supportive of a tropical storm. Recent ASCAT and OSCAT passes, while not showing the strongest winds, still how a well-defined center. The current storm info, satellite image, and microwave image can be found below.

11:00 PM PDT Sun Jun 30
Location: 17.1°N 104.8°W
Moving: NW at 10 mph
Min pressure: 1001 mb
Max sustained: 45 mph

Forecast for TS Dalila
The forecast for TS Dalila isn't an easy one, as shown by what has already happened. What has been a seemingly favorable environment for intensification has caused some problems for Dalila, but they seem to be going away. SHIPS analysis still shows very warm SST's for the next two days with modest ocean heat content. It keeps SST's above the 26C threshold for 3 1/2 days, plenty of time for intensification. Wind shear is still expected to stay low. SHIPS indicates below 15kts for the entire forecast period, but it initialized with just 3kts of shear while UW-CIMSS has between 10-15kts. I still think no matter what that wind shear shouldn't prevent, at least, steady strengthening for the next several days. Finally, SHIPS shows 700mb-500mb relative humidity values between 55% and 65% for the entire forecast period. Precipitable water values are also favorable for development as they indicate no dry air. Dalila is still a compact system, with TS force winds extending not that far from the center. This means Dalila can feel fluctuations in intensity greater, upward or downward. This means if an inner core can get fully established, which one is trying to, then quicker intensification is still possible. I am lowering my peak intensity for Dalila slightly due to what happened today. I am still higher than the NHC forecast and intensity guidance, but I feel with the environment Dalila is in she can make it higher than a minimal hurricane. After two to three days, I expect weakening to begin as the cyclone moves over cooler waters with no ocean heat content. Since the environment should stay relatively moist and with lower shear values, weakening shouldn't be overly quick. Whether the NHC/intensity models or me and a couple other Wunderbloggers are right is to be seen.

The track forecast isn't as complicated as the intensity one is for Dalila. The pattern is easy to identify and there is more model agreement. TS Dalila has been going to plan pretty well track-wise. She is making the turn t the NW as expected as the weakness closes. As the system gets further north it will only feel the impacts of the "death ridge" more. This ridge is responsible for record heat in the SW US and intensification of wildfires. One wildfire has sadly claimed the lives of 19 firefighters, which makes this the largest loss of firefighters since 9/11. Anyway, this ridge is large and deep. Dalila is expected to turn toward the WNW and then W as it gets buried into the cyclonic flow. In the short term, global, dynamical, and statistical models agree that Dalila won't make landfall and that she will turn to the west over the next few days. After that there is some differences in how much of a turn occurs. The GFS and its ensembles show a more westerly track while the CMC and ECMWF show more southwesterly track after 3 days or so. The dynamical and statistical models aren't sold on either of the solutions. Until one solution begins to take hold on the models, I'll continue to show a western track, but with a slight bend to the SSW. No matter what the track is in a few days, Dalila is still expected to bring impacts to Mexico. Heavy rain, flooding, gusty winds, and increased waves/rips are expected along and in from the coast. All interests in south-central Mexico need to be taking precautions as impacts from Dalila will be felt. Tropical storm warnings and watches are in effect for some areas and that information, along with my intensity and track forecasts, can be found below.

Warning and watch info:




Intensity forecast:

INIT 01/0700Z 40 KT 45 MPH
12H 01/1800Z 45 KT 50 MPH
24H 02/0600Z 50 KT 60 MPH
36H 02/1800Z 65 KT 75 MPH
48H 03/0600Z 75 KT 85 MPH
72H 04/0600Z 65 KT 75 MPH
96H 05/0600Z 55 KT 65 MPH
120H 06/0600Z 45 KT 50 MPH

Track forecast:

Have a good night/morning everyone and I'll try to have a new update on Dalila late today or early tomorrow. Another Epac storm is also possible in the coming days and so is an Atlantic tropical cyclone from a trough split. These are thing I will try to mention tomorrow, but I may not have enough time to do so.

Tropical Storm Dalila Tropical Hurricane Epac


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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I'm a CMU Honors student and love meteorology and extreme weather. I've been fascinated by weather since I was 5, and plan on becoming a meteorologist

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