Tropical Storm Julian

Post Tropical Storm Julian Track 0300 Hours August 30 2021
Post Tropical Storm Julian Track 0300 Hours August 30 2021

Tropical Storm Julian Wind Speed FieldTropical Storm Julian –  NWS National Hurricane Center Miami FL 300 AM GMT Mon Aug 30, 2021 (see video below)

Julian has been showing signs of a transition into an extratropical cyclone over the past several hours. The deep convection has become detached to the northeast from the low-level center and cloud tops of that convection are warming. A line of convection to the south of the center resembles a frontal boundary, with recent scatterometer data showing a notable wind shift along that line. Based on the structural changes noted above, as well as a majority of FSU phase-space diagrams from the various global models, Julian is estimated to have transitioned to an extratropical cyclone. Recent ASCAT data showed the cyclone’s intensity remains 50 kt. The cyclone is forecast to maintain this intensity through Monday before weakening. It is then forecast to dissipate in a few days over the northern Atlantic. The system should continue to move quickly northeastward through Monday, then turn northward and northwestward Monday night into Tuesday.

This is the last advisory on Julian by the National Hurricane Center. 

FORECAST POSITIONS AND MAX WINDS

INIT  30/0300Z 38.1N  41.9W   50 KT  60 MPH - Post Tropical (WSW Vila do Corvo,Azores)
 12H  30/1200Z 40.3N  39.0W   50 KT  60 MPH - Post Tropical (WNW Vila do Corvo,Azores)
 24H  31/0000Z 44.1N  36.4W   50 KT  60 MPH - Post Tropical (WNW Vila do Corvo,Azores)
 36H  31/1200Z 48.5N  36.2W   45 KT  50 MPH - Post Tropical (ENE St. John's,NF Canada)
 48H  01/0000Z 53.0N  38.2W   40 KT  45 MPH - Post Tropical (ESE Charlottetown,NF Canada)
 60H  01/1200Z 57.0N  40.0W   40 KT  45 MPH - Post Tropical (ESE Nanortalik,Greenland)

NWS National Hurricane Center Miami FL 900 PM GMT Sun Aug 29, 2021 

The convective pattern and structure of Julian has remained consistent throughout today, with the low-level center remaining tucked under the southwestern edge of a deep convective mass and good outflow in the northeastern semicircle. A late morning ASCAT-C overpass sampled peak winds of 45 to 47 kt, and since the cyclone has likely intensified slightly since that time, the initial intensity has been increased to 50 kt. Julian is now moving quickly to the northeast, or 050/21 kt in southwesterly flow to the south of a deep-layer area of low pressure located just east of Newfoundland. The storm is forecast to continue to move northeastward at a similar forward speed through Monday, and then begin to turn northward then northwestward Monday night through Tuesday as the cyclone moves around the periphery of the larger low. The model track guidance continues to be in excellent agreement on this scenario, and the latest NHC track forecast is little changed from the previous one.

A cold front associated with the low east of Newfoundland has already begun to interact with the circulation of Julian, as noted by dry air being pulled into the southern portion of the circulation, and linear banding developing to the south of the cyclone. Baroclinic forcing could allow for some slight additional strengthening through tonight. However, Julian should cross the 26 C isotherm this evening, and reach waters of 22 C by 24 h while interacting with the cold front and associated mid- to upper level trough to its north. These factors should cause the cyclone to go through extratropical transition tonight through tomorrow morning, with the transition complete by late tomorrow. The latest SHIPS guidance as well as the FSU phase-space diagrams depict this transition scenario. Once extratropical, the system should dissipate within a couple of days over the north Atlantic. The latest NHC intensity forecast was essentially an update of the previous one, and is close to the HCCA and IVCN solutions.

FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 36.7N  44.6W   50 KT  60 MPH - Tropical Storm (WSW Ponta Delgada,Azores)
 12H  30/0600Z 38.8N  41.4W   55 KT  65 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 24H  30/1800Z 42.2N  38.1W   55 KT  65 MPH - Post Tropical (WSW Vila do Corvo,Azores)
 36H  31/0600Z 46.3N  36.8W   50 KT  60 MPH - Post Tropical (WSW Brest,France)
 48H  31/1800Z 51.0N  37.7W   45 KT  50 MPH - Post Tropical (WSW St. John's,NF Canada)
 60H  01/0600Z 55.0N  39.6W   40 KT  45 MPH - Post Tropical (ESE Nanortalik,Greenland)
 72H  01/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Sun Aug 29, 2021 

The system has become better organized this morning, with the low-level center located on the southwestern edge of a persistent mass of deep convection. A 1246 UTC ASCAT-B pass revealed an area of winds over 40 kt southeast of the center, so the system is upgraded to Tropical Storm Julian with maximum winds of 45 kt.

Julian is accelerating toward the northeast (045/15 kt) in the flow to the south of a deep-layer area of low pressure located just east of Newfoundland. The storm is expected to move around the southeastern and eastern periphery of this large low during the next few days, accelerating further and turning toward the north by 48 hours. The track models are all in good agreement on this scenario, and the NHC track forecast is very close to the TVCA and HCCA consensus aids. This new forecast is also relatively unchanged from the previous advisory.

Winds in the storm have increased faster than expected, even in the face of 20 kt of west-southwesterly shear. This shear is forecast to increase substantially in the coming days, with SHIPS diagnostics indicating it may reach magnitudes of 40-50 kt. However, the storm will still be moving over marginally warm waters around 26 degrees Celsius, and its fast motion and some baroclinic forcing could allow for additional strengthening during the next 12-24 hours. Nearly all the intensity models support some strengthening, and the NHC official forecast peaks the winds at 55 kt in 24 hours, roughly between the IVCN and HCCA solutions. Phase-space diagrams suggest that Julian will probably already be going through extratropical transition at that time, and it should be fully extratropical by 36 hours. Gradual weakening is anticipated after 24 hours, and the extratropical low is likely to dissipate over the north Atlantic by day 3.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 35.1N  46.8W   45 KT  50 MPH - Tropical Storm (ENE St. George's,Bermuda)
 12H  30/0000Z 36.9N  43.7W   50 KT  60 MPH - Tropical Storm (WSW SCdF,Azores)
 24H  30/1200Z 40.0N  39.7W   55 KT  65 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  31/0000Z 43.6N  37.0W   50 KT  60 MPH - Post Tropical (WNW Vila do Corvo,Azores)
 48H  31/1200Z 48.0N  36.8W   45 KT  50 MPH - Post Tropical (WSW Dingle,Ireland)
 60H  01/0000Z 52.2N  38.2W   40 KT  45 MPH - Post Tropical (WSW Galway,Ireland)
 72H  01/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 PM AST Sat Aug 28, 2021 

This afternoon’s satellite presentation consists of an exposed surface circulation with a rather shapeless convective mass displaced to the east and north of the center. Without question, the 15 to 20 kt of west-northwesterly shear is doing a number on the cloud pattern. Also evident, are a number of arc clouds propagating away from the system’s deep convection, certainly indicative of dry air intrusion. Consequently, the initial intensity is once again held at 30 kt for this advisory.

The global models as well as the Decay SHIPS (ECMWF/GFS) intensity guidance still show the shear relaxing a bit tonight and into Sunday, which should allow the depression to briefly become a tropical storm. By Monday, however, the shear is forecast to increase while the cyclone moves into an even more dry and stable air mass. These inhibiting contributions should stifle further strengthening and weaken the cyclone back to a depression through the remainder of the forecast period. It’s worth mentioning that the GFS indicates that the depression will become a remnant low in 72 hours while turning northwestward to west-northwestward within the tradewind flow and dissipate by the end of the week. For now, the NHC forecast will stick with the consensus intensity models and the SHIPS guidance which agree on maintaining a depression through day 5.

The initial motion is estimated to be northward, or 360/7 kt. The depression remains embedded in low- to mid-level southerly flow produced by a mid-Atlantic trough dominating the central Atlantic. This synoptic feature, along with a subtropical high pressure located over the east Atlantic and western Africa, should influence a generally northward motion through the 5-day period. The official track forecast again is adjusted a little to the right of the previous advisory beyond day 3, and lies between the TVCN and HCCA multimodel solutions.

FORECAST POSITIONS AND MAX WINDS

INIT  28/2100Z 15.6N  50.0W   30 KT  35 MPH - Depression (WSW Speightstown,Barbados)
 12H  29/0600Z 16.6N  50.0W   35 KT  40 MPH - Tropical Storm (WSW Grand Bay,Dominica)
 24H  29/1800Z 18.2N  49.9W   35 KT  40 MPH - Tropical Storm (WSW Grand Bay,Dominica)
 36H  30/0600Z 19.8N  49.7W   30 KT  35 MPH - Depression (ESE Philipsburg,Saint Martin)
 48H  30/1800Z 21.3N  49.3W   30 KT  35 MPH - Depression (ENE Anguilla,BVI)
 60H  31/0600Z 22.5N  48.8W   30 KT  35 MPH - Depression (ENE Anguilla,BVI)
 72H  31/1800Z 23.8N  49.0W   30 KT  35 MPH - Depression (ENE Anguilla,BVI)
 96H  01/1800Z 27.2N  50.5W   30 KT  35 MPH - Depression (ESE St. George's,Bermuda)
120H  02/1800Z 30.5N  51.5W   30 KT  35 MPH - Depression (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL  500 AM AST Sat Aug 28, 2021 

The tropical wave and associated low-pressure system that the NHC has been tracking for the past several days has finally acquired a well-defined surface circulation and enough organized deep convection to be classified as a tropical depression. The last few visible satellite images yesterday evening indicated a tight swirl in the low-cloud field and a 27/2325Z partial ASCAT-A pass showed the circulation was also well-defined, albeit with only 23-kt surface winds. Since the time of that scatterometer pass, however, a significant increase in deep convection with cloud tops colder than -80 deg C has developed very near and to the northeast of he center, with a few cells also now having developed just to the southwest of the center. Based on the structure noted in the ASCAT data and the pronounced increase in the amount and organization of the convection, the advisory intensity is estimated to be 30 kt.

The initial motion estimate is 340/06 kt. The system has slowed down markedly during the past several hours, likely due to the sharp increase in the associated convection. A turn toward the north is forecast to begin later this afternoon as the system moves into a break in the Atlantic subtropical ridge pattern, with a general northward motion continuing through the remainder of the forecast period. The latest NHC model guidance is surprisingly in good agreement on this track scenario, with only minor forward speed differences noted between the models.

The 18-20 kt of westerly vertical wind shear affecting the depression is expected to abate somewhat during the next 12-24 hours, which should allow for some slight strengthening to occur while the system moves over 27.5 deg C sea-surface temperatures. By 48 hours, however, the shear is forecast to increase again in excess of 25 kt, which should act to weaken the cyclone, possibly even causing it to degenerate into a remnant low. For now, however, the official intensity forecast calls for the system to remain a tropical depression at days 3 and 4 in the event the cyclone regenerates at day 5 when the shear is forecast to decrease below 10 kt, which may allow for convection to redevelop. The official intensity forecast closely follows a blend of the intensity consensus models IVCN and NOAA-HCCA.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0900Z 14.0N  49.9W   30 KT  35 MPH - Depression (WSW Speightstown,Barbados)
 12H  28/1800Z 14.8N  50.3W   35 KT  40 MPH - Tropical Storm (WSW Grand Bay,Dominica)
 24H  29/0600Z 16.1N  50.3W   35 KT  40 MPH - Tropical Storm (WSW Grand Bay,Dominica)
 36H  29/1800Z 17.7N  50.2W   35 KT  40 MPH - Tropical Storm (WSW St. John’s,A&B)
 48H  30/0600Z 19.1N  50.0W   30 KT  35 MPH - Depression (ESE Philipsburg,Saint Martin)
 60H  30/1800Z 20.7N  49.7W   30 KT  35 MPH - Depression (ENE Anguilla,BVI)
 72H  31/0600Z 21.9N  49.7W   30 KT  35 MPH - Depression (ENE Anguilla,BVI)
 96H  01/0600Z 24.5N  50.5W   30 KT  35 MPH - Depression (ENE Anguilla,BVI)
120H  02/0600Z 27.5N  52.8W   30 KT  35 MPH - Depression (ENE Anguilla,BVI)

NWS National Hurricane Center Miami FL 800 PM EDT Fri Aug 27, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane Ida, located over western Cuba.

  • 1. An elongated area of low pressure located over the central Atlantic several hundred miles east of Bermuda is producing disorganized showers and a couple of thunderstorms. Environmental conditions are expected to be only marginally conducive for development, however, a tropical depression could still form by early next week. By midweek, the system is forecast to be absorbed by a frontal system. The disturbance is expected to drift eastward through tonight and Saturday, then accelerate northeastward Sunday toward the central north Atlantic. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…60 percent.
  • 2. Satellite images indicate that an area of low pressure has developed in association with a tropical wave located several hundred miles east of the Lesser Antilles. However, shower and thunderstorm activity is limited near the center of the low. Some additional development of this system is expected, and a tropical depression is likely to form Saturday or Saturday night before it moves into an environment of stronger upper-level winds and slightly cooler waters. The disturbance is forecast to move west-northwestward through tonight, then turn northward Saturday. * Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…80 percent.
  • 3. Another tropical wave is expected to emerge off of the west African coast by the middle of next week. Afterwards, environmental conditions appear marginally conducive for gradual development toward the end of next week as the system moves west-northwestward to northwestward at 10 to 15 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Fri Aug 27, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on recently upgraded Hurricane Ida, located over the northwestern Caribbean Sea near the Isle of Youth.

  • 1. An elongated area of low pressure located over the central Atlantic several hundred miles east of Bermuda is producing disorganized showers and a couple of thunderstorms. Environmental conditions are expected to be marginally conducive for development, however, a tropical depression could still form over the weekend. The system is expected to drift eastward through tonight and Saturday, then accelerate northeastward Sunday toward the central north Atlantic. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…60 percent.
  • 2. Showers and thunderstorms associated with a tropical wave located about midway between the Cabo Verde Islands and the Lesser Antilles have become a little better organized today. Additional development of this system is expected, and a tropical depression is likely to form later tonight or Saturday before it moves into an environment of stronger upper-level winds and slightly cooler waters. The disturbance is forecast to move west-northwestward through tonight, then turn northward Saturday. * Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high...80 percent.
  • 3. Another tropical wave is expected to emerge off of the west African coast by the middle of next week. Afterwards, environmental conditions appear marginally conducive for gradual development toward the end of next week as the system moves west-northwestward to northwestward at 10 to 15 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low...20 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Thu Aug 26, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on recently upgraded Tropical Storm Ida, located over the northwestern Caribbean Sea.

  • 1. An elongated area of low pressure located over the central Atlantic about 650 miles east of Bermuda is producing disorganized showers and thunderstorms. Environmental conditions are forecast to be generally conducive for development, and a tropical depression is likely to form over the weekend. The system is expected to move slowly eastward during the next day or two, but a faster northeastward motion is forecast to begin on Sunday. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high…70 percent.
  • 2. A tropical wave located about midway between the Cabo Verde Islands and the Lesser Antilles continues to produce a large area of disorganized showers and thunderstorms. Gradual development of this system is expected, and a tropical depression is likely to form during the next couple of days before it moves into an environment of stronger upper-level winds and slightly cooler waters. The disturbance is forecast to move west-northwestward for another day or so and then turn northward over the weekend. * Formation chance through 48 hours…medium…60 percent. * Formation chance through 5 days…high…70 percent.

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