Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 8:05 AM GMT on August 25, 2014
Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.
Tropical Storm Cristobal continues to meander near the southeastern Bahamas. As of the latest NHC intermediate advisory, the following information was posted on the cyclone:
Wind: 50 mph, with higher gusts
Location: 24.5°N 72.9°W
Pressure: 998 mb
Cristobal is generating some very deep convection this evening over the western Atlantic and adjacent Bahama islands, which is likely producing some very heavy rain and winds to tropical storm force across the southeastern portion of the archipelago. A reconnaissance aircraft has been investigating Cristobal this morning; the highest reported surface wind speed from the SFMR instrument aboard the plane has been around 45 kt, and there were flight-level winds as high as 55 kt in the large convective band southeast of the center. The National Hurricane Center took this into account and bumped up the initial intensity to 45 kt at 6z. Since that time, deep convection has begun to consolidate around the center, with cloud tops as cold as -70C to -80C enveloping the cental gyre. There is a good equatorial outflow jet due to the more favorable upper wind environment in that area, but it remains poor to the north due to about 20 kt of northerly shear on the backside of the deep continental ridge over the eastern United States.
Figure 1. Latest infrared satellite image of Tropical Storm Cristobal. Image credit: NOAA's Satellite Services Division (SSD).
Data from the aircraft, along with satellite, scatterometer, and microwave data suggest that the center of Cristobal has reformed a bit to the south, closer to the deep convection in an environment of less shear; this is not uncommon of weak, sprawling systems struggling to establish an inner core. Since the center appears to be a little farther south, some more intensification could occur in the short-term than was predicted by the NHC at 0300Z given the more favorable environment where the center relocation occurred. Most of the guidance makes Cristobal a hurricane in a few days, and my forecast will follow suit. I was tempted to go a little higher than 70 kt given the expected acceleration of Cristobal in the mid-latitude westerlies at later times, and also due to possibly increased upper divergence ahead of a shortwave mid- to upper-level trough providing ascent, but I withheld given the uncertainties in the trough to cyclone interaction. Most of the global models show Cristobal interacting with a frontal zone near Atlantic Canada by day five, so extratropical status is shown by then. It should be noted that the guidance generally doesn't seem eager to kill off Cristobal too quickly during the post-tropical stage, and it is likely that the system will remain a strong gale center for several days subsequent to extratropical transition.
As previously mentioned, a slew of data this morning indicates that Cristobal's center has reformed to the south of what the 0300Z NHC position was. Looking into the crystal ball, I see that the models did not substantiate a center reformation, which will throw off the 6z model runs. It is uncertain what implications this will have on the track, but I suspect any changes will be near term ones, not longer term. Because of the center reformation and the global models' now erroneous initialization of the storm, my forecast is significantly to the west of the model consensus TVCN, and the National Hurricane Center, particularly during the first couple of days, showing an initial northwestward motion before turning the cyclone into the westerlies. It is also slower than the NHC and much of the guidance as a result. While it is highly unlikely Cristobal moves back west under the ridge and makes landfall along the United States coast, there is a nonzero chance of this happening if the cyclonicity over the western Atlantic continues to weaken; currently there is a surge of strung out moisture to the north of Cristobal which could serve as the impetus for cyclonicity, with a small upper low not far to the north of that, which could also enhance the large-scale cyclonicity in the area and pull Cristobal slowly northward. This is the solution of the global models, but while they appear to be handling the synoptic pattern rather nicely, I do not know if Cristobal will interact as strongly with the reinforced cyclonicity as that guidance suggests, since again, their initialization was faulty due to the center relocation. UW-CIMSS synoptic steering data and water vapor imagery show that a small weakness still remains to the north of the storm, but it appears to be closing, at least temporarily. If the ridge ends up stronger than forecast in the near-term, Cristobal could go even farther west than I have indicated below, possibly significantly so. Having said all of that, recurvature remains the most viable option by far, and I give it a 10% chance that Cristobal will reform far enough south or the ridge will close off enough to induce a westward motion toward the United States coast. A gradual turn toward the east-northeast will acceleration is forecast later in the period as the cyclone gets caught up in the circulation of a mid-latitude trough now over the upper midwest.
I am not confident in the short-term track forecast.
Initial 08/25 0600Z 24.5°N 72.9°W 45 kt 50 mph
12 hour 08/25 1800Z 24.7°N 73.2°W 45 kt 50 mph
24 hour 08/26 0600Z 25.0°N 73.3°W 50 kt 60 mph
36 hour 08/26 1800Z 25.3°N 73.5°W 55 kt 65 mph
48 hour 08/27 0600Z 26.1°N 73.9°W 60 kt 70 mph
72 hour 08/28 0600Z 32.2°N 70.8°W 70 kt 80 mph
96 hour 08/29 0600Z 37.9°N 67.9°W 70 kt 80 mph
120 hour 08/30 0600Z 42.4°N 52.0°W 60 kt 70 mph: extratropical
Figure 2. My forecast track for Cristobal.
Karina continues to wind down under high shear. As of the 0300Z NHC advisory, the following information was available on Karina:
Wind: 45 mph, with higher gusts
Location: 17.5°N 129.3°W
Movement: E at 9 mph
Pressure: 1002 mb
After losing all deep convection near 0z, there has been a regeneration of fairly cold convection about 30 miles to the west of the center, confined to that direction due to strong easterly shear associated with outflow from large Hurricane Marie, which is dominating much of the eastern Pacific at this time.
Figure 3. Latest infrared satellite image of Tropical Storm Karina. Image credit: NOAA's Satellite Services Division (SSD).
As long as Karina maintains some semblance of deep convection, regardless of how much it will undoubtedly pulsate, the cyclone will remain a tropical cyclone. However, water vapor and satellite data show the already strong shear giving way to even stronger shear as Karina moves counterclockwise around the larger circulation of Marie. Most of the guidance except for the ECMWF and HWRF show the circulation of Karina being absorbed into Marie in about 48 hours, and I have chosen to follow the guidance that assimilates the cyclone quicker.
Karina is following the NHC forecast track closely, and my own track is not significantly different from theirs due to lack of reasons to be. Karina is forecast to move steadily into the larger circulation of Maria, ultimately becoming entrained into the south side of the powerful hurricane in a day or two.
Initial 08/25 0300Z 17.5°N 129.3°W 40 kt 45 mph
12 hour 08/25 1200Z 17.4°N 128.6°W 30 kt 35 mph
24 hour 08/26 0000Z 17.3°N 127.7°W 25 kt 30 mph: post-tropical/remnant low
36 hour 08/26 1200Z 16.9°N 126.3°W 20 kt 25 mph: post-tropical/remnant low
48 hour 08/27 0000Z: absorbed by Marie
Figure 4. My forecast track for Karina.
After becoming a Category 5 earlier on Sunday, Marie has weakened, but only a little. As of the 0300Z NHC advisory, the following information was posted on the hurricane:
Wind: 150 mph, with higher gusts
Location: 16.6°N 112.8°W
Movement: WNW at 12 mph
Pressure: 927 mb
Category: 4 (Saffir-Simpson Hurricane Wind Scale)
Satellite images suggest little change to the cloud pattern of the powerful hurricane over the last several hours. The small eye was cloud-filled around 6z up until about 7z, but recent images indicate it has cleared out again. Satellite estimates suggest that the hurricane may be a little weaker now, however. Upper-tropospheric outflow remains well-defined and the water beneath the hurricane remains quite warm.
Figure 5. Latest infrared satellite image of Hurricane Marie. Image credit: NOAA's Satellite Services Division (SSD).
Marie likely peaked in intensity Sunday evening when it hit 140 kt, and the hurricane is likely to steadily decline from this point onward. While there has been little change to the eye or the central dense overcast, satellite and microwave data this morning shows that the deep convective band emanating to the south of the large hurricane is gradually wrapping cyclonically closer to the inner core/CDO area, which could possibly be a precursor to a concentric eyewall cycle. The eye has not contracted enough for me to believe that yet, however, and if such a process is in the cards, it will probably take another 12 to 18 hours to complete. Waters remain around 29 to 28C underneath the hurricane until about 36 hours, when they begin to cool. A faster rate of weakening is expected at that point, with remnant low status shown by day four when Marie moves over cold waters in the high latitudes of the Pacific. However, I suspect the large circulation of Marie, similar to Lowell a few days ago, will be slow to spin down, so I've decided to carry tropical storm force winds with it even as it loses its convection and becomes a remnant low in 96 hours.
Satellite fixes indicate that Marie has been smoothly following the track of the National Hurricane Center and the model consensus. Assuming there are no temporal wobbles due to complex mesoscale processes inside the eyewall, Marie should follow a fairly smooth path around a large subtropical ridge to the north from southwestern Mexico to off the Pacific United States coastline. The global models show a small break in the ridge as Marie enters high latitudes at days four and five, so I've shown a subtle poleward bend between 72 and 96 hours in order to reflect this. However, my forecast track remains to the left of the model consensus since Marie will be a weak system at those times.
Of note, Marie is the first Category 5 to form in the eastern north Pacific since Hurricane Celia of 2010.
Initial 08/25 0300Z 16.6°N 112.8°W 130 kt 150 mph
12 hour 08/25 1200Z 17.4°N 114.7°W 125 kt 145 mph
24 hour 08/26 0000Z 18.2°N 115.7°W 115 kt 135 mph
36 hour 08/26 1200Z 19.2°N 117.3°W 100 kt 115 mph
48 hour 08/27 0000Z 20.3°N 119.2°W 95 kt 110 mph
72 hour 08/28 0000Z 22.1°N 123.5°W 65 kt 75 mph
96 hour 08/29 0000Z 24.4°N 128.6°W 40 kt 45 mph: post-tropical/remnant low
120 hour 08/30 0000Z 28.3°N 133.7°W 30 kt 35 mph: post-tropical/remnant low
Figure 6. My forecast track for Marie.
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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