Wxchaser97's Tropical Weather Blog

Tropical Storm Erin forms, Invest 92L less likely to develop

By: wxchaser97, 5:16 PM GMT on August 15, 2013

Tropical Storm Erin
The 2013 Atlantic hurricane season's 5th named storm, TS Erin, formed earlier this morning just south of the Cape Verde Islands. Tropical Depression 05L formed yesterday from a strong tropical wave that came off the African continent a couple days ago. It also had help of a CCKW passing through the region. This wave was able to develop a surface low, not attached to the ITCZ, and get organized convection developing over the center. ASCAT and OSCAT passes have shown a tight circulation with winds slowly increasing. This, along with TAFB numbers at TS strength, have supported the upgrade to TS Erin from TD-5. Right now, there is one area of deep convection over the small center. Erin also has one band feeding into the main convective area. TAFB is currently at T2.5/35kts, SAB is at T2.0/30kts, and CIMSS ADT has T3.3/51kts, but ADT didn't locate the actual center of the Erin. TS Erin has brought some gusty winds and rain showers to parts of the Cape Verde Islands, which prompted tropical storm warnings for a while, but these conditions are subsiding as Erin moves away from the islands. The latest NHC info sand satellite image can be found below.

11:00 AM AST Thu Aug 15
Location: 14.4°N 26.5°W
Moving: WNW at 15 mph
Min pressure: 1006 mb
Max sustained: 40 mph

Forecast for Erin
TS Erin has a good environment to strengthen in right now, but that will change in a couple days. Erin is over warm SST's and expected to remain over favorable SST's for another day or so. SHIPS analysis has Erin over 27.1C waters, but it has Erin moving over more marginal waters in about a day. As Erin moves farther west later in forecast period, SST's should increase to higher levels. Wind shear is currently low to moderate over Erin. This means that convection isn't getting sheared away from the llc, thus the upper level profile is decently favorable for development. Shear may increase a little as Erin gets farther north, but it won't be the end of Erin. After about day 5, shear should lessen as it gets away from an ull to it's north. The TUTT should be moving to the north and weakening, which is normal at this time of year, making a more favorable environment in the Caribbean and SW Atlantic as shear lessens. Erin has a decent moister envelop at the moment. SHIPS analyzed RH values in the mid 70% range. This is due to Erin feeding off the ITCZ and just a moist environment overall in that area. As Erin moves farther to the WNW, it will encounter a more drier and more stable environment later in the forecast period. Erin will be over warmer waters, which may offset some of the effects of the dry air. It also depends as to how far north Erin gets as to how much dry air the system contends with. If it stays at a more southerly path, it won't eat as much dry air and SAL as it would if it went farther north. Intensity models are pretty spread out on how Erin will strengthen or weaken. Our more reliable intensity models take Erin to a strong TS, while other models have it a moderate to weak TS. The GFS and ECMWF dissipate Erin during the forecast period as they send it farther north into the more dry air and SAL. Erin reminds me of Dorian with conditions never being greatly favorable or greatly unfavorable, but the environment is a little more conducive for strengthening with Erin than Dorian. My intensity forecast is similar to the NHC's, but I maintain a moderate TS at the end of the period instead of weakening to a weak TS. There is a chance that Erin doesn't survive the dry air, but this will be dealt with later.

The track forecast for Erin is uncertain in the latter part of the forecast period, just like the intensity forecast. Erin is currently moving WNW at 15mph. Erin is being steered by a subtropical ridge to its north and northwest. An upper-level low directly to the north of Erin is causing a weakness that is tugging Erin to the WNW. The east-to-west flow around the ridge to its north would cause a westward motion if it wasn't for the weakness. As the low moves out and the ridge expands a little, Erin should move on a more westward trek. However, models aren't in agreement on this westward motion happening. The ECMWF and GFDL, along with some other dynamical/statistical models are showing Erin turn more to the NW. The GFS, HWRF, and a majority of the dynamical/statistical models are showing a more west movement in the later portion of the forecast period. Since Erin will be a shallow system, it will be steered by the low-level flow around the ridge. This means that the early turn to the NW most likely won't happen. My track forecast is similar to the NHC's. It is still too far out to speculate whether Erin will be a long range threat to the US, if it survives. While most Cape Verde storms don't hit the US, the pattern has been one that favors US landfalls this year. Unless a trough comes at the right time to pick up whatever remains of Erin, it may be a threat to impact the US. Erin will also come close to the Lesser Antilles.

Intensity Forecast

INIT 15/1500Z 35 KT 40 MPH
12H 16/0000Z 40 KT 45 MPH
24H 16/1200Z 45 KT 50 MPH
36H 17/0000Z 45 KT 50 MPH
48H 17/1200Z 50 KT 60 MPH
72H 18/1200Z 50 KT 60 MPH
96H 19/1200Z 45 KT 50 MPH
120H 20/1200Z 45 KT 50 MPH

Track Forecast


Invest 92L
Invest 92L is a tropical wave that is producing disorganized showers and thunderstorms. Yesterday at this time, it looked like we had a developing tropical depression on our hands. There was a strong mid-level spin and convection was developing and expanding over this area. It was, and still is, in a favorable environment with low shear, warm SST's and moist air. It looked like we'd have a tropical cyclone heading into the Yucatan Peninsula if organization trends had continued. However, 92L was lacking a well-developed surface low and surface convergence. This meant that the system wouldn't be able to sustain convection. consequently, when DMIN, when instability between the water and the air above is at its lowest, invest 92L lost most of its convection. It also showed us that there wasn't much going on at the surface. I really don't know why 92L wasn't able to get a well-defined surface low going over favorable conditions. The chances of this developing into a tropical cyclone have lessened since it didn't organize like it could've overnight. Convection has fired again over 92L, but it remains disorganized. There may be a weak surface low just off the coast of the Yucatan Peninsula, but it is too little too late. Whatever is going on at the surface will come ashore soon. Several recon flights are scheduled to investigate 92L today, so we may get a better idea of what's going on and where it may go. If 92L wants to develop into a tropical cyclone, it'll have to do it in the Gulf Of Mexico. Shear will still be low to moderate, with SST's being very warm and the air remaining moist. If it develops, it would only probably be able to become a moderate TS at best. Where this system goes is still anyone's guess. Models are split on whether 92L continues WNW into Mexico or turns to the north and hits the central gulf coast. Since 92L is still weak, it is a little more likely for the main energy to go WNW. Heavy rain will impact the gulf coast whether or not a tropical cyclone makes landfall up there as a strong trough will be able to pull up moister from 92L. this is the same trough that may steer 92L to the north, especially if it was more organized. The progress of 92L will be monitored over the next several days to see if it develops and where it does. The current ATCF info and satellite image can be found below.

Chance of development in the next 48hrs: 50%

AL, 92, 2013081512, , BEST, 0, 188N, 876W, 25, 1008, DB, 34, NEQ, 0, 0, 0, 0, 1010, 200, 80, 0, 0, L, 0, , 0, 0, INVEST, M,

Have a great day everyone and I'll have a new update on Erin and 92L tonight or tomorrow. More tropical waves are expected to come off Africa and they could develop into TC's. Erin should knock out some of the dry air in the way and it looks like the CV season has started. With a MJO pulse coming as well, it looks like we are getting into an active period for a while. We will probably get our first hurricane before month's end. Doesn't look like this season will bust, ha!

Updated: 8:38 PM GMT on August 15, 2013


The Dorian is back, but not for long; Gil still unorganized

By: wxchaser97, 6:17 PM GMT on August 03, 2013

Tropical Depression Dorian
I can't believe I'm saying this, but Dorian is back as a tropical cyclone. After finally establishing a low-level center yesterday, it was able to sustain deep convection. Since the remnants met the criteria for a tropical cyclone, they were upgraded to TD Dorian. Winds were near TS, but the NHC elected to have TD sustained and higher than usual gusts. Dorian developed at about the latest it could've. The window for development was closing as high wind shear from the north was going to hit the system today. If it took any longer for Dorian to organize, I'm not sure the NHC would've designated it. Dorian is already not looking like it was earlier. The wind shear I just mentioned has stripped the LLC of it's convection and MLC. Since Dorian is just a naked swirl, it will likely be downgraded to a remnant low in the next 6-12hrs, depending if any areas of convection try to develop one last time. The MLC and associated convection is still back just north of the Bahamas and off the east coast of FL. They will continue to bring some rain and gusty winds to parts of the far northern Bahamas, the central-east coast of FL, and the waters in this region. Dorian will be absorbed into the frontal trough off the east coast in the next 24-48hrs and not be a threat to the US or to redevelop. It won't redevelop since it will be dealing with very high mid to upper level wind shear and it'll be in a baroclinic environment. This should be my last update on Dorian in whatever form it's in. My intensity and track forecast is the same as the NHC's. The latest NHC advisory and satellite image can be found below.

11:00 AM EDT Sat Aug 3
Location: 30.6°N 78.4°W
Moving: NE at 14 mph
Min pressure: 1013 mb
Max sustained: 35 mph

Tropical Storm Gil
Tropical Storm Gil remains disorganized as it heads to the west. Gil was once a strengthening hurricane, but it was hit with some wind shear which tilted the circulation and caused the convection to become disorganized. The convection is having a hard time keeping up with the low-level center and there are no banding features present. SAB, TAFB, and Dvorak T#'s are still falling due to the lack of organization of Gil. The latest NHC advisory info and satellite image can be found below.

8:00 AM PDT Sat Aug 3
Location: 15.0°N 132.6°W
Moving: W at 12 mph
Min pressure: 999 mb
Max sustained: 60 mph

Forecast For Gil
The forecast for Gil is rather bleak. Gil is expected to continue to weaken as it heads off to the west. Wind shear is expected to continue to impact Gil negatively for at least the next few days. As it heads off farther to the W it may encounter slightly cooler waters and stabler air. However, waters will still be marginal so it won't weaken as quickly as if it was farther north. Intensity models are spread out as to how fast Gil will weaken. Going based off of experience and model guidance, I think Gil will weaken slowly but steadily. My intensity forecast is similar to the NHC's. TS Gil is still in the east to west flow on the south side of the deep-layer ridge to the north. It may build back to the southwest a little, forcing Gil to move WSW for a little bit. This ridge will continue to steer Gil for the entire forecast period. The model guidance is all in agreement in the track of Gil. My forecast track is just an update of the last one. TS Gil will be too far south to bring wind or rain to Hawaii.

INIT 03/1800Z 50 KT 60 MPH
12H 04/0600Z 45 KT 50 MPH
24H 04/1800Z 45 KT 50 MPH
36H 05/0600Z 40 KT 45 MPH
48H 05/1800Z 40 KT 45 MPH
72H 06/1800Z 35 KT 40 MPH
96H 07/1800Z 35 KT 40 MPH
120H 08/1800Z 35 KT 40 MPH

Have a great day and I'll have a new update tomorrow. I know the update is kind of short, but there isn't much new about Gil.


Gil unexpectedly weakening, Invest 91L trying to develop one last time

By: wxchaser97, 12:52 AM GMT on August 03, 2013

Tropical Storm Gil
Just as it looked like Gil was headed back in the right direction for strengthening, another curve ball is thrown. When I did my last entry, Gil was poised to strengthen into a strong Cat-1 or minimal Cat-2 hurricane. The reliable intensity models where showing this and it looked like the environment supported it. However, a little while after I finished my last entry the convection collapsed over Gil. While new convection has refired, it isn't as organized as earlier convection. There isn't any organized banding features and upper-level outflow isn't impressive. Also the low-level center and the mid-level center look to be displaced. This is confirmed by microwave imagery and vorticity maps. My guess is that there may be some shear impacting Gil, along with the low-level flow pushing out the LLC a little faster than the MLC is moving. Some dry air might have also been able to get into Gil, but RH values are back on the rise. As a result of the pretty ragged appearance of Gil, SAB and TAFB T#'s have been coming down. The latest NHC advisory, based off of satellite/microwave images and decreasing T#'s, has Gil now down to a 60kt TS. I have little reason to argue against this, but I am disappointed that Gil is weakening instead of strengthening like I hoped. The latest NHC advisory data and satellite image can be found below.

2:00 PM PDT Fri Aug 2
Location: 14.6°N 129.4°W
Moving: W at 9 mph
Min pressure: 992 mb
Max sustained: 70 mph

Forecast For Gil
The intensity forecast for Gil has flip-flopped over the past couple days. At first, I thought my intensity forecast was a little too bullish and that I'd have to revise downward. Then, it looked like Gil would remain in a more favorable environment for longer, and thus I had more confidence in Gil becoming a weak Cat-2 hurricane, or at least a strong Cat-1. However, Gil pulled a fast one and now it doesn't look like it'll strengthen again. If Gil was still going to plan, we'd probably have a stronger Cat-1 hurricane right now. The air around Gil is moistening up and SST's are favorable. SHIPS diganostic message says 700-500mb RH values are in the mid 60% range and climbing, signaling a decently moist environment. It also analyzed SST's to be at 27.3°C, which is favorable for TC development, and SST's maps confirm this. SHIPS say shear is between 5-10kts, but UW-CIMSS shear maps says between 10-25kts. Looking at satellite loops, there does look to be some shear being imparted on Gil, but it doesn't look to be lethal or turn particularly lethal over the next few days. Based off of the environmental factors and recent trends with Gil, I think it will slowly weaken over the next 2 days before more steady weakening takes over. This will be attributed to marginally cooler SST's and more stable air. All of the intensity models are showing weakening from here on out and I think they are correct this time.

The one thing with Gil that hasn't changed is its track forecast. TS Gil is moving to the W at 9mph. Gil is still being steered by the deep-layer ridge to its north. Gil is caught up in the east-to-west flow on the south side of the ridge.There hasn't been much, if any, change in this pattern and the storm is expected to remain in this flow for a while. The dynamical and statistical models agree that, in the short-term, Gil should continue to the west. After a couple days, they diverge with some going to the NW while other W or SW. Given with how the low-level flow is and where the majority of the dynamical and global models take Gil, a turn to the WSW in a few days is pretty likely. Gil should remain far enough south of Hawaii so that it feel no wind or rain impacts.

Forecast Intensity
INIT 02/2300Z 60 KT 70 MPH
12H 03/1200Z 55 KT 65 MPH
24H 04/0000Z 55 KT 65 MPH
36H 04/1200Z 50 KT 60 MPH
48H 05/0000Z 45 KT 50 MPH
72H 06/0000Z 35 KT 40 MPH
96H 07/0000Z 30 KT 35 MPH
120H 08/0000Z 25 KT 30 MPH

Forecast Track

Watch/Warning/Advisory Info

Invest 91L
Invest 91L is back, again! These remnants have been very persistent coming through the SW Atlantic. While there was a strong MLC with disorganized convection, there was no surface convergence which meant no LLC. An upper-level-low was creating shear over 91L which wasn't helpful for it to develop. Because Dorian had decoupled and degenerated a few days before it got to the TUTT, it wasn't able to generate enough latent heat to bust the trough. Now that the ULL has backed away to the SW, there is a more favorable upper-level environment for 91L to develop in for the next day. Right now, 91L is situated over the gulf stream so SST's aren't an issue. The air is moist around the invest as well. The environment will only be conducive for the next 12-24hrs before moderate to high wind shear from the north starts impacting 91L. Of course, you need a low-level-center to be able to use the favorable environment fully. For the past week, convection would fire during D-MAX and then dissipate during D-MIN since there is no surface convergence to hold it together. Today, the tides finally changed. A surface low has been forming over the past several hours just off the Florida coast. Satellite and radar shows it becoming better defined with some banding featured developing. Surface pressures are falling and observations from Florida and the Bahamas support that a closed low is developing. If recent trends continue we could get a tropical depression or storm before wind shear increases. If we do get a tropical cyclone, it would be Dorian because the remnants have been clearly traceable for a while. 91L is headed off to the NNE, albeit slowly. It should then be accelerated off to the NE when it gets absorbed by the trough to the north. The global, dynamical, and statistical models are in agreement of the track for 91L. Invest 91L is bringing gusty winds and some rain to Florida and the Bahamas, but shouldn't be much more serious than that.

Chance of development in the next 48hrs: 50%

I'll have a new blog tomorrow on TS Gil and 91L, especially if it regenerates.


Hurricane Gil heading west while intensifying

By: wxchaser97, 6:14 AM GMT on August 02, 2013

Hurricane Gil
Hurricane Gil is headed away from North America and is back on a strengthening trend. Yesterday featured Gil's convection waning some and the inner core becoming a little ragged. Now, however, Gil is trying to build back up its inner core and there have been some deep convective bursts. This has caused TAFB to come up to T5.0/90kts and SAB to T4.5/77kts. UW-CIMSS ADT is at T3.5/55kts, but it is under the impression that Gil is less organized than it is. A solid outflow pattern is still noted with Gil showing that the upper-level air patter remains favorable. There also remains well pronounced spiral banding features with Gil. The storm still retains a tight circulation based on recent scattometer passes and has a pretty small wind diameter. The latest NHC advisory places Gil as a 75kt hurricane. They would've gone higher if it wasn't for the somewhat ragged appearance on satellite, and I think Gil may be a bit stronger. The latest NHC advisory info and satellite image can be found below.

8:00 PM PDT Thu Aug 1
Location: 14.4°N 126.4°W
Moving: W at 14 mph
Min pressure: 985 mb
Max sustained: 85 mph

Forecast For Gil
The intensity forecast for Gil has changed since my last blog entry. It now looks like Gil should remain in a favorable environment for longer, thus maintaining it's intensity for longer. Wind shear isn't expected to become an issue for the next 5 days and SST's won't cool down as fast. Looking at SHIPS analysis and SST maps, SST's should remain plenty favorable for the next 3 days before becoming more marginal later in the forecast period. Since the model guidance is farther south, they think Gil will remain away from the higher shear belt in the Epac. Hurricane Gil should also keep it's ULAC for a while, helping defend Gil from shear and ventilate the storm. 700-500mb RH values are a tad lower than they were yesterday. However, the air around Gil is expected to moisten up a little as RH values climb back into the mid to upper 60s. The intensity guidance says Gil should have a few days to remain a hurricane before the cooler waters/slightly more stable air begin to take their toll and weaken the storm. My intensity forecast still calls for Gil to reach low-end Cat-2 strength and then slowly, but steadily, weaken afterward. This is higher than the NHC forecast, but given the favorable environment and the more reliable intensity models solutions, I think a Cat-2 is still pretty likely.

The track forecast for Gil remains relatively unchanged since yesterday. Hurricane Gil has made more of a turn to the west and is moving along at a modest pace, 14mph. The main steering component remains the same from yesterday and will throughout the entire forecast period. Gil is caught up in the east-to-west flow from the deep-layer ridge to its north. This ridge is expected to move along with Gil, keeping him enveloped in the east-west flow for a while. In fact, looking at steering maps and the models, Gil may turn a little WSW late in the forecast period. The global, dynamical, and statistical models agree in the short-term that Gil will remain on its westward track. After a couple days, some of the dynamical and statistical models diverge to the north and south. Since most of the dynamical suite and the global models show a W-WSW component at the end of the period, plus steering maps supporting this, I now have a turn to the WSW at days 4 and 5. Since Gil will remain pretty far south, Hawaii won't be under the gun for tropical cyclone impacts this time around. The hurricane should just harmlessly weaken and dissipate before it can get to any land areas. It should get far enough west while remaining a TC to get into the territory of the CPHC.

Forecast Intensity
INIT 02/0600Z 75 KT 85 MPH
12H 02/1800Z 80 KT 90 MPH
24H 03/0600Z 85 KT 100 MPH
36H 03/1800Z 85 KT 100 MPH
48H 04/0600Z 80 KT 90 MPH
72H 05/0600Z 65 KT 75 MPH
96H 06/0600Z 50 KT 60 MPH
120H 07/0600Z 45 KT 50 MPH

Forecast Track

Watch/Warning/Advisory Information


Have a great day and I'll have a new update on Gil sometime tomorrow. I'll also try to do a separate blog about invest 91L and other interests in the Atlantic.


Hurricane Gil intensifying over the open Pacific

By: wxchaser97, 6:31 AM GMT on August 01, 2013

Hurricane Gil
The Eastern Pacific is once again active with the season's 7th named storm. It is also the season's 5th hurricane to form. Gil formed from a disturbance from the monsoon trough in a very favorable environment. With the MJO being in a positive phase in the epac, there is enhanced moisture and lift for storms to use, combined with very warm SST's and a favorable upper level pattern, has resulted in good tropical cyclonegenesis conditions. Hurricane Gil had an eye trying to pop out on visible satellite late yesterday, but that eye then got covered by deep convection. Microwave imagery from earlier also showed this eye. While the latest available microwave image shows not much left of the eye, I do expect it to come back pretty soon. Gil has well pronounced banding features and solid upper-level outflow. The latest satellite intensity estimates from TAFB are 4.5, SAB at 4.0, and UW-CIMSS ADT at 3.2. ADT fails to realize that Gil is more organized then ADT thinks it is and thus is giving out a lower T#. The current storm info and satellite image can be found below.

8:00 PM PDT Wed Jul 31
Location: 14.2°N 121.8°W
Moving: WNW at 12 mph
Min pressure: 990 mb
Max sustained: 80 mph

Forecast for Gil
Hurricane Gil has a pretty predictable future ahead of it for intensities. The environment should be plenty favorable for further intensification before conditions become more hostile farther to the north and west. This has been the similar story for most of the Epac cyclones this year. Gil has been rapidly intensifying for the past day. This has caused the intensity forecasts to be bumped up from what they first were and put a little uncertainty into the current ones. Gil is situated in an environment that has very warm SST's, low vertical wind shear, and modest moister values. SHIPS diagnostic message and UW-CIMSS analysis maps show that shear is at or below 10kts over Gil. Depending on how far north Gil gets over the next day or so determines how strong the shear will be over it. If it goes farther north it will encounter more of the higher shear area, but if it stays farther south then it won't deal with as much shear. SST's are very warm right now, with SHIPS initializing Gil over 28C+ temps. Once again, it depends on how far north Gil goes in the forecast period to determine how cool the SST's will get. They fully favor further strengthening right now, but they will get marginal later in the period. 700-500mb Relative Humidity (RH) values should remain around 60% for the entire forecast period, which is moist, but not overly moist. After several days of favorable conditions, Gil should encounter marginal SST's and higher shear which will induce weakening. My forecast is a little above the intensity guidance and mostly in line with the NHC, except a little higher on the peak strength. It should be noted that if Gil gets its core more organized again, RI may resume. If RI resumes it is possible that Gil becomes a strong Cat-2 to low end Cat-3. The NHC gives Gil a 13% chance of becoming a category 3 hurricane while I give Gil a 25% chance.

The track forecast for Hurricane Gil is pretty cut-and-dry without a lot of variables. Gil is currently, and has been, heading west-northwest. Gil is caught up in the west west-northwest flow from the subtropical ridge to its north. This has been the primary steering agent for all of Gil's life and will continue to be. After about 3 to 4 days, the reliable global models show a trough digging down into part of the ridge and weakening it. This will cause a weakness in the ridge and will impact the track and forward speed of Gil. Gil will slow it's forward speed and possibly take a small jog to the north. After going through the weakness created by the trough, Gil should get back in the dominate low-level easterly flow and thus back on a due west path. The statistical, dynamical, and global models mostly agree on where Gil will go, besides some longer range differences. My track forecast is pretty close to the NHC track and model guidance. Hurricane Gil shouldn't impact any land as it will be too far south to bring anything toward Hawaii.

Forecast intensities
INIT 01/0300Z 70 KT 80 MPH
12H 01/1200Z 80 KT 90 MPH
24H 02/0000Z 85 KT 105 MPH
36H 02/1200Z 80 KT 90 MPH
48H 03/0000Z 75 KT 85 MPH
72H 04/0000Z 70 KT 80 MPH
96H 05/0000Z 55 KT 65 MPH
120H 06/0000Z 45 KT 50 MPH

Forecast Track

Watch/Warning/Advisory Information

Have a great morning and I'll be back with a new update, plus a short update on the Atlantic, late today.

Updated: 7:18 AM GMT on August 01, 2013


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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