Wxchaser97's Tropical Weather Blog

Arthur becomes season's first hurricane, expected to reach category 2 intensity

By: wxchaser97, 4:32 PM GMT on July 03, 2014

Hurricane Arthur
Arthur has organized nicely since 4:00AM EDT, when I wrote my last blog. Since early this morning, Arthur has built its inner core and closed off its eyewall. The circulation has become even more symmetrical and there are numerous rainbands feeding into the circulation. Radar has also indicated some lightning strikes in the eyewall, which indicates strengthening. Satellite presentation has also become much better. A small eye is now apparent on satellite and upper-level cirrus is improving on the western semicircle. Convection is deeper, more sustained, and more symmetrical than it was several hours ago. Aircraft recon has recorded 80kt surface winds with their SFMR instrument. Satellite estimates from TAFB and SAB are up to T4.5/77kts as well, and the NHC has Arthur at a current intensity of 80kts. The latest NHC advisory info and satellite image can be found below. The NRL site is still having internet issues so loading satellite and microwave images is spotty at best.


11:00 AM EDT Thu Jul 3
Location: 32.4°N 78.5°W
Moving: NNE at 10 mph
Min pressure: 981 mb
Max sustained: 90 mph




Forecast For Arthur
I have to say that I was surprised that Arthur got its act together quickly and strengthened like this, but it wasn't totally unexpected. As I had mentioned earlier, if Arthur had organized its inner core fast enough, then it would be able to strengthen more than what I or the NHC had expected. The HRRR showed this solution and had brought Arthur up to category 2 strength in 15 hours when I last wrote my blog. Well, Arthur has organized it's inner core nicely. The eyewall is almost close to, most of the time, closed and has limited dry air from entraining into the circulation. Arthur is still in a favorable environment for strengthening. SST's are still very warm, currently around 28°C according to a nearby buoy. SST's are expected to stay at or above 26°C for the next 18-24hrs. As Arthur pulls away from NC, SST's begin to drop off dramatically. The cold SST's north of the gulf stream will begin to induce weakening and help with a change to an extratropical cyclone. Wind shear is also running low currently. In fact, anticyclonic flow is looking more organized that when I wrote my previous blog. This is helping to increase the upper-level divergence over Arthur and decrease the shear over the system. Shear should remain low for the next 24 hours before increasing ahead of the incoming mid to upper-level trough. The shear will be destructive to the convection and begin to tear the circulation apart. However, Arthur will be getting into the right-entrance region of this trough soon, which will maximize upper-level divergence over the system. This should help get Arthur even stronger before it turns extratropical. Due to low SST's, high shear, and baroclinic energy getting added to Arthur, an extratropical transition is in store in about 2 days. Arthur will continue to weaken once it becomes an extratropical cyclone and interact with land and a larger extratropical cyclone. My forecast intensity is being pushed upward due to the steady strengthening of Arthur. 90mph was my previous peak, but with Arthur already reaching that it has to be raised. My new forecast peak is 105mph, but it is possible that Arthur could even peak 5 or 10mph stronger.

Arthur has had a general motion off to the north-northeast. There have been some wobbles to the north that have brought Arthur closer to the coast. In fact, the motion over the past hour or so was more northward. Arthur is still expected to turn to the northeast and accelerate ahead of the deep-layer trough advancing from the NW. Model guidance is still tightly clustered in the short-term, but looks to be slightly farther west. With how Arthur still hasn't fully made the NE turn yet, it is likely that Arthur at least makes landfall along the Outer Banks. A landfall would occur in about 18hrs or so as Arthur continues a steady northeast path. The northward motions have brought Arthur closer the the Carolina Coast. If Arthur doesn't make the NE soon, then it is possible that Arthur makes landfall on mainland NC. While most of the guidance doesn't show a mainland NC landfall, I wouldn't rule it out. The 12z GFS brings Arthur very close to Wilmington, NC before turning off to the NE, which is something to keep an eye on. After passing NC, the track of Arthur looks to be fairly certain. As it interacts with the deep-layer trough, it will continue to move off to the NE and accelerate. A landfall in Nova Scotia in just over 48hrs looks on track and then moving into NF after that. My forecast track is moved slightly more westward/northward in the short-term to account for Arthur being farther north than I expected and for the small shift in guidance. My cone does include the Wilmington area and, as mentioned earlier, it is possible for a landfall or very close pass there before moving over the Outer Banks. Rain and gusty winds are already being reported over Eastern SC and Southern NC. More rain and stronger winds should spread into NC as the day progresses, especially if Arthur tacks closer to the coast/makes a mainland landfall. The Outer Banks are still expected to receive the worst weather with Arthur. Strong winds, possibly hurricane-force sustained, moderate to heavy rain, and between 3-6' of storm surge can be expected. Other areas along the Eastern US can receive 1-3' of storm surge and some rain, especially in the far NE as Arthur interacts with the trough.

Forecast Intensity
INIT 03/1630Z 80 KT 90 MPH
12H 04/0000Z 85 KT 100 MPH
24H 04/1200Z 90 KT 105 MPH
36H 05/0000Z 80 KT 90 MPH
48H 05/1200Z 70 KT 80 MPH...POST-TROP/EXTRATROP
72H 06/1200Z 55 KT 65 MPH...POST-TROP/EXTRATROP
96H 07/1200Z 40 KT 45 MPH...POST-TROP/EXTRATROP
120H 08/1200Z 30 KT 35 MPH...POST-TROP/EXTRATROP


Forecast Track



Watches/Warnings/Advisories
A HURRICANE WARNING IS IN EFFECT FOR...
* SURF CITY NORTH CAROLINA TO THE NORTH CAROLINA/VIRGINIA BORDER
* PAMLICO SOUND
* EASTERN ALBEMARLE SOUND

A HURRICANE WATCH IS IN EFFECT FOR...
* LITTLE RIVER INLET TO SOUTH OF SURF CITY

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* SOUTH SANTEE RIVER SOUTH CAROLINA TO SOUTH OF SURF CITY
* THE NORTH CAROLINA/VIRGINIA BORDER TO CAPE CHARLES LIGHT
VIRGINIA...INCLUDING THE MOUTH OF THE CHESAPEAKE BAY
* WESTERN ALBEMARLE SOUND

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE
AND PROPERTY SHOULD BE RUSHED TO COMPLETION.

A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE POSSIBLE
WITHIN THE WATCH AREA. ANY DEVIATION OF THE FORECAST TRACK TO THE
LEFT...OR AN INCREASE IN THE FORECAST SIZE OF ARTHUR WOULD LIKELY
REQUIRE THE ISSUANCE OF HURRICANE WARNINGS FOR ALL OR PART OF THE
HURRICANE WATCH AREA.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA.

INTERESTS ALONG THE UNITED STATES EAST COAST NORTH OF THE WARNING
AREA...PRIMARILY IN SOUTHEASTERN NEW ENGLAND...SHOULD MONITOR THE
PROGRESS OF ARTHUR.

INTERESTS IN NOVA SCOTIA SHOULD MONITOR THE PROGRESS OF ARTHUR.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY YOUR
LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICE.


Have a great Thursday and I'll have another blog late tonight.

*Disclaimer* My forecasts are not official. For making any important decisions, seek the NHC and NWS for all forecasts and statements. Listen to local emergency management when evacuation orders are issued.

Atlantic Hurricane Arthur

Updated: 4:36 PM GMT on July 03, 2014

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Tropical Storm Arthur a threat to the East Coast, near hurricane strength

By: wxchaser97, 8:01 AM GMT on July 03, 2014

Tropical Storm Arthur
Tropical Storm Arthur is nearing hurricane strength off the Florida/Georgia border. The storm has had it struggles over the past couple days. When I did my last blog, TS Arthur was still a struggling invest. It had a defined, but weak, surface low and had meager convection. The low wasn't able to sustain/organize the convection and dry air was becoming a problem. The low began to deepen, which increased the low-level convergence and then the upper-level divergence. Convection began to increase and become slightly more organized around the strengthening low. Dry air prevented sustained deep convection from forming on the northern side of the low. As organizational trends continued, it looked certain that the disturbance would become a tropical cyclone. Early on Tuesday morning, at 0300z, the NHC declared invest 91L as Tropical Depression 01L. Dry air continued to limit significant organization of the system. Later that morning, a weather station on Grand Bahama Island recorded sustained winds of 33kts and TD 1 was upgraded to Tropical Storm Arthur. Convection continued to slowly organize throughout the day and into the night. While the storm was organizaing, it still had a complex structure. The mid-level center, with an associated eye feature, was located to the east of the low-level center. The llc, and some vort maxes, would remain dislocated until it all began to consolidate under the convection more. Further strengthening continued on Wednesday as the cloud pattern became more organized, convection tried to become deeper on the western side, and the wind field expanded. While dry air was still an issue, Arthur was trying to mix it out. With an inner core still not fully established, dry air was still able to entrain into the circulation and prevent much strengthening. Now, Arthur is still dealing with the same issue. Dry air has been periodically getting entrained into the circulation through the western semicircle. This is has prevented the inner core from becoming fully closed and deep convection on the western side. Radar is showing that the eyewall is about 60%-75% closed. The precipitation looks more symmetrical than yesterday and there are numerous rain bands feeding into the circulation. Deep convection is firing on the northern side of Arthur and is trying to wrap around the entire circulation. Upper-level cirrus is pretty pronounced on the eastern semicircle with little cirrus expanding out of the western semicircle. Any eye has periodically been seen on satellite and the convection looks to be expanding. TAFB and SAB estimates place Arthur at 65kts. SSD ADT and UW-CIMSS ADT are running higher, about 75-80kts. Recon is en route to investigate Arthur once again. I suspect that they will find Hurricane Arthur with 65kt, maybe 70 but more likely 65, max sustained winds. The latest NHC advisory info, satellite imagery, and microwave imagery can be found below. Of note, the NRL site is having internet issues so the satellite image may or may not be working fully until later today.


2:00 AM EDT Thu Jul 3
Location: 30.9°N 79.1°W
Moving: N at 8 mph
Min pressure: 988 mb
Max sustained: 70 mph







Forecast For Arthur
The intensity forecast for Arthur is not clear-cut. Arthur is in a very favorable thermodynamic environment. Residing over anomalously warm waters, there is more than enough energy for Arthur to tap into. SHIPS shows that SST's should remain at or above 26°C for the next 36 hours. Buoy data suggests that SST's are even warmer than what SHIPS indicates in some areas. Wind shear is also ranging from light to moderate. Upper-level outflow is strongest on the western side of Arthur, evident on satellite and UW-CIMSS analysis. Wind shear should lessen a little for the next 2 days. Wind shear abating some will help ease some of the dry air issues and ventilate Arthur even more. Global models show the slight improvement in the anticyclonic pattern aloft, but then begin to degrade it closer to 36-48hrs. Wind shear shouldn't cause much of a problem to Arthur even if it slightly increases again. On the other hand, dry air will still be an issue in the short-term. Water vapor imagery shows a region of dry air to the north and west of Arthur. Additionally, sounding data from Jacksonville, Miami, and Charleston still shows some dry air in the mid-levels. The air isn't as dry as yesterday though, as relative humidity values were as lower than 40% in some parts of the atmosphere. Still, the dry air is clearly having an adverse impact on Arthur. The dry air has caused the eyewall to be open and convection not as deep on the western side. As mentioned earlier, Arthur is trying to change that. How fast Arthur can fully develop its inner core/close off its eyewall will determine how much strengthening Arthur can do in the next 36hrs. If the eyewall were to close off right now and prevent dry air from entraining into the circulation, then we would see Arthur likely become a solid category 2 hurricane. Should Arthur continue to slowly close the eyewall, but do it in about the next 12hrs, Arthur should begin to see an increase in intensity and become at least a solid category 1 hurricane. If dry air won out and Arthur never fully developed its inner core, I can't see Arthur becoming much more than a minimal category 1. The last solution is unlikely as Arthur is slowly making strides in overcoming its dry air issues. The global and hi-res models reflect the first two options. The HRRR closes off the eyewall quickly and intensifies Arthur to a category 2 hurricane in 15hrs. The HWRF and ECMWF are slower to build the inner core and don't intensify Arthur as much, only to a strong cat-1 to maybe borderline cat-2. The GFS, at a lower resolution, doesn't have Arthur's current strength correct, so it only makes Arthur a weak cat-1. If the GFS was at a higher reolution, then it would probably show something close to the ECMWF/HWRF in terms of strength. My thinking is that Arthur will continue to slowly intensify, with a quickening in pace tomorrow. In about 24-30hrs, Arthur will make it's closest approach to the US. A possible landfall is in store, especially along the Outer Banks. After that, Arthur will continue to move NE. SST's will become cold north of the Gulf Stream and shear will increase ahead of an approaching trough. This said trough will , on the other hand, increase upper-level divergence over Arthur as Arthur gets in the right-entrance region of the trough. The increased upper-level divergence will increase/sustain convection, but with the cool SST's, increasing shear, and baroclinic energy, Arthur will begin to weak and turn extratropical in 60-72hrs. My intensity forecast is a blend of the LGEM, SHIPS, HWRF, and the ECMWF. It is close to the NHC's, except I am forecasting a peak of 90mph. It is possible that if Arthur can organize fast enough, then it could become a category 2 hurricane.

The track forecast is more simpler than the intensity forecast, but it still has it's challenges. Arthur has still not made the anticipated northeasterly turn. Recon from 6 hours ago, satellite fixes, and the latest recon show a motion that is due north. There have been some westerly, and some easterly, jogs in the current motion for about the past 6-8 hours, but Arthur has been generally moving due north. A look at water vapor imagery shows the upper-level trough approaching from the northwest. Arthur should begin to make the turn soon as it gets caught up in its steering current. UW-CIMSS steering maps show that Arthur should be making that turn at any time. While we know that Arthur will begin making the NE turn soon, the continued northerly motion has implications on the future track. My guess is that the convection firing and wrapping around the western side is tugging Arthur just to the west of what was expected. With Arthur running a tad father north, it'll be very close to making landfall with NC, especially the Outer Banks. I think a landfall on Cape Hatteras is likely, but a landfall on the mainland of NC is low. Model guidance is pretty close on where Arthur will go. There isn't much spread and not many models bring Arthur into mainland NC. After making a potential landfall with the Outer Banks, Arthur will continue off to the northeast under the influence of the mid to upper-level trough. Models begin to diverge on how it will interact with an extratropical cyclone to its north, but it looks likely that Arthur will make landfall in Nova Scotia. My track forecast is a blend between the dynamic and global models, and is just a tad west of the NHC's.

Tropical Storm Arthur will have impacts on North Carolina and the rest of the Mid-Atlantic Coast, the NE, and parts of Canada. The worst impacts will be in coastal NC where hurricane warnings are already issued. A landfall on on the Outer Banks is very possible and the worst conditions will be felt here. TS force-sustained winds and hurricane-force gusts are likely with heavy rain and storm surge flooding. There is a chance that sustained hurricane-force winds are felt on Cape Hatteras. Highway 12, and it's protection, will be put to the test for the first time since Irene. A mandatory evacuation has been order for all people on Hatteras Island to be off by 5am. Voluntary evacuations are in order for other areas of the Outer Banks. Rip currents are a big threat to all areas of the East Coast for the nest few days. The St. Augustine, FL Life Guard preformed 11 rip current rescues yesterday alone, and due to the nature of people and tourists, I expect more rescues on affected beaches. Since Arthur will be relatively fast-moving when it is passing NC, rainfall will be kept to a minimum. Only up to 3" or so of rain is expected for far eastern NC. Parts of the NE could get up to an inch of rain when Arthur interacts with the incoming trough. Nova Scotia and NF should get heavy rain and gusty winds from Arthur.


Forecast Intensity
INIT 03/0800Z 60 KT 70 MPH
12H 03/1800Z 70 KT 80 MPH
24H 04/0600Z 75 KT 85 MPH
36H 04/1800Z 80 KT 90 MPH
48H 05/0600Z 70 KT 80 MPH...BECOMING EXTRATROP
72H 06/0600Z 55 KT 65 MPH...POST-TROP/EXTRATROP
96H 07/0600Z 40 KT 45 MPH...POST-TROP/EXTRATROP
120H 08/0600Z 35 KT 40 MPH...POST-TROP/EXTRATROP


Forecast Track



Watches/Warnings/Advisories
A HURRICANE WARNING IS IN EFFECT FOR...
* SURF CITY NORTHWARD TO DUCK
* PAMLICO SOUND
* EASTERN ALBEMARLE SOUND

A HURRICANE WATCH IS IN EFFECT FOR...
* LITTLE RIVER INLET TO SOUTH OF SURF CITY

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* SOUTH SANTEE RIVER SOUTH CAROLINA TO SOUTH OF SURF CITY
* NORTH OF DUCK TO CAPE CHARLES LIGHT VIRGINIA...NOT INCLUDING
CHEASEPEAKE BAY
* WESTERN ALBEMARLE SOUND

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE
AND PROPERTY SHOULD BE RUSHED TO COMPLETION.

A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE POSSIBLE
WITHIN THE WATCH AREA...IN THIS CASE WITHIN THE NEXT 24 HOURS. ANY
DEVIATION OF THE FORECAST TRACK TO THE LEFT...OR AN INCREASE IN THE
FORECAST SIZE OF ARTHUR WOULD LIKELY REQUIRE THE ISSUANCE OF
HURRICANE WARNINGS FOR ALL OR PART OF THE HURRICANE WATCH AREA.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA.

INTERESTS ALONG THE UNITED STATES EAST COAST NORTH OF THE WARNING
AREA...PRIMARILY IN SOUTHEASTERN NEW ENGLAND...SHOULD MONITOR THE
PROGRESS OF ARTHUR.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY YOUR
LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICE.



Have a great Thursday and I'll have another blog on Arthur tonight/early tomorrow morning. I won't be able to do one until late on the 4th/early on the 5th due to watching fireworks.

*Disclaimer* My forecasts are not official. For making any important decisions, seek the NHC and NWS for all forecasts and statements. Listen to local emergency management when evacuation orders are issued.

Atlantic Hurricane Tropical Storm Arthur

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About wxchaser97

I'm in high school and love meteorology and extreme weather. I've been fascinated by weather since I was 5, and I plan on becoming a meteorologist.