Tropical weather analysis - May 26, 2012
Beryl
Let's get right down to it: this is unusual. Nearly unprecedented even. Subtropical Storm Beryl formed off the coast of the Carolinas late Friday evening. According to historical records, the last time two named storms occurred in May was during 1887. It should be noted that there is little correlation to early season activity with the rest of the season. However, I am finding it increasingly difficult to believe CSU's April forecast of a mere 10 named storms. Besides that, the pattern this year favors more homegrown storms than we have seen in recent years, which might help to inflate the numbers somewhat. When the eastern Atlantic is shut down (which we should expect, due to increasing westerly shear associated with the oncoming El Nino), tropical waves tend to wait until reaching a more favorable longitude before transforming into tropical cyclones. This has been the case so far in 2012, with Alberto and Beryl both forming in the western Atlantic less than 200 miles from the United States coast.
As of the latest NHC advisory, the following was posted on Beryl:
Wind: 45 mph, with higher gusts
Location: 32.4°N 75.1°W
Movement: W at 2 mph
Pressure: 1001 mb
Category: Subtropical storm (Saffir-Simpson Hurricane Scale)
The center remains exposed to the east of a large band of deep convection that is just grazing the North Carolina Outer Banks. Convection is virtually nonexistent over the cyclone center at this time, but recent satellite and long-range doppler radar loops suggest this convection may be slowly attempting to wrap into the center. Also, some weak upper-level outflow has developed on the western flank of the circulation.
Figure 1. Latest infrared satellite image of Subtropical Storm Beryl, courtesy of NOAA's Satellite Services Division (SSD).
Vertical shear over the system is decreasing, outflow is developing, and examination of water vapor and satellite imagery suggests that Beryl is dismantling itself from the trough to the east. This triple point gives me reason to believe that Beryl may transition to a tropical storm sooner rather than later, although earlier AMSU microwave data still indicated a mostly cold core system. Additionally, the cyclone is still caught beneath an upper low, particularly well-defined from 300 to 100 mb. This may temporarily slow the transformation process.
The mid-level flow over the central United States is quickly becoming zonal, which is helping to push the ridge southward to the east of Beryl. Simultaneously, the cyclone is being influenced by the aforementioned trough. A combination of the northeasterly flow on the east side of the ridge, and the northwesterly flow on the west side of the trough is effectively preventing much movement. However, since Beryl is drifting west, the ridge is clearly becoming the dominant steering mechanism. As the mid-level flow over the storm strengthens, Beryl is expected to respond by accelerating and moving west-southwest or southwest. Then, on Sunday, a westward turn toward the southeast United States is expected as the cyclone rounds the southern periphery of the Atlantic ridge. I am a bit to the south of the model consensus, and agree pretty strongly with what the National Hurricane Center is currently saying.
Beryl is expected to move back into the Atlantic on late Tuesday or early Wednesday as it begins to feel the influence of a deep-layered trough forecast to amplify across the central United States on Monday. Analysis of upper-level winds during that time suggest that some reintensification is possible, although how much of that will be tropical or baroclinic remains to be seen.
Interests along the southeast United States from South Carolina to northern Florida should monitor the progress of Beryl.
5-day intensity forecast
Initial 05/26 0300Z 40 KT 45 MPH
12 hour 05/26 1200Z 40 KT 45 MPH
24 hour 05/27 0000Z 45 KT 50 MPH...BECOMING TROPICAL
36 hour 05/27 1200Z 50 KT 60 MPH
48 hour 05/28 0000Z 55 KT 65 MPH...NEAR THE NORTHERN FLORIDA COAST
72 hour 05/29 0000Z 35 KT 40 MPH...INLAND
96 hour 05/30 0000Z 30 KT 35 MPH...INLAND
120 hour 05/31 0000Z 30 KT 35 MPH...OVER WATER
I am not too enthusiastic about a quick inland decay rate, since the system is forecast to stall after landfall, which will put it in close proximity to the warm waters of the Gulf Stream. It should also be noted that there is considerable uncertainty in my intensity forecast, since predicting tropical transition is rather difficult. Also, cyclones in this part of the world tend to, more often than not, ingest dry continental air into their circulations, which can interrupt the strengthening process.
5-day track forecast
Figure 2. My 5-day forecast track for Beryl.
Given quasi-stationary movement expected after landfall, Beryl has the potential to produce flash flooding across portions of the southeast United States into early next week.
Watches and warnings
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* VOLUSIA/BREVARD COUNTY LINE FLORIDA TO EDISTO BEACH SOUTH CAROLINA
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* EDISTO BEACH TO SOUTH SANTEE RIVER SOUTH CAROLINA
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.
A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED STATES...
INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST
OFFICE.
Bud
As quickly as it strengthened, Bud has fallen apart. As of the latest NHC advisory, the following was posted on the decaying cyclone:
Wind: 50 mph, with higher gusts
Location: 20.2°N 105.8°W
Movement: N at 7 mph
Pressure: 1002 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)
Even being completely free of convection, the center of Bud is difficult to locate, to say the least. In fact, the cyclone resembles a post-tropical remnant low, rather than a tropical cyclone. Nonetheless, Dvorak constraints disallow for abrupt weakening, which is the likely reason the National Hurricane Center has decided to keep Bud as a tropical storm for now. In any case, the system has become very disorganized, with satellite imagery indicating that the mid-level is racing northward, leaving the low-level center behind.
Figure 3. Latest infrared satellite image of Tropical Storm Bud, courtesy of NOAA's Satellite Services Division (SSD).
Given the disheveled satellite appearance, as well as the fact that a portion of the circulation is already overland, Bud has probably dissipated. What's left of the low-level circulation should quickly decouple over the mountainous terrain of western Mexico.
Although I have indicated a westward turn today, given the close interaction with the rugged terrain, a more plausible scenario is probably that the cyclone, or its remnants, will move erratically until losing their identity in about 24 hours. It might not even take that long.
All watches and warnings will likely be lowered on the next NHC advisory.
5-day intensity forecast
Initial 05/26 0300Z 45 KT 50 MPH
12 hour 05/26 1200Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
24 hour 05/27 0000Z 20 KT 25 MPH...DISSIPATED
5-day track forecast
Figure 4. My 5-day forecast track for Bud.
Watches and warnings
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM MANZANILLO WESTWARD TO CABO CORRIENTES
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM NORTH OF CABO CORRIENTES TO SAN BLAS
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA.
A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.
Bud still poses a heavy rainfall threat given its proximity to the Pacific, but it is likely that any serious flood potential will be mitigated by the lack of convection.
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