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Hurricane JIMENA Forecast Discussion Number 14

2015-08-30 04:51:23| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SAT AUG 29 2015 000 WTPZ43 KNHC 300251 TCDEP3 HURRICANE JIMENA DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 800 PM PDT SAT AUG 29 2015 Jimena continues to undergo an eyewall replacement, with significant inner-core structural changes seen in satellite data throughout the day. Microwave images show a small inner eyewall rotating around an irregularly-shaped outer eyewall at about 60 n mi radius, the latter which could be slowly contracting. Although Jimena's cloud pattern has fluctuated some during this period of inner-core change, its overall organization has remained about the same since the last advisory. Satellite classifications seem to bear this out, with intensity estimates of T6.0/115 kt and T6.5/127 kt from SAB and TAFB, respectively, at 0000 UTC. These are blended with the latest UW-CIMSS ADT value of 6.1/117 kt to keep the initial intensity estimate at 120 kt. The intensity forecast is challenging. The large-scale environment is forecast to remain relatively favorable during the next day or two, apart from some north-northwesterly shear associated with a cold low to the northeast of Jimena. This could allow an opportunity for reintensification if the current eyewall replacement fully plays out, but predicting intensity fluctuations due to inner-core dynamics is nearly impossible and beyond the scope of this forecast. Thus, a slow decrease in intensity is indicated in the new forecast as large-scale conditions only gradually become less conducive. This is a blend of the statistical-dynamical guidance. As Jimena gradually gains latitude later in the forecast period, global models show a minor increase in westerly shear while other thermodynamic factor remain generally neutral, except for slowly decreasing SSTs. These factors suggests a slow decay of the cyclone, and the new intensity forecast is in agreement with the latest multi-model consensus that shows a monotonic decrease in intensity from days 3 to 5. The eye of Jimena has been wobbling quite a bit, but smoothing through these yields a faster initial motion estimate of 295/11. Jimena should continue moving west-northwestward during the next few days as it approaches the western end of a subtropical ridge around 140W. A weakness in the ridge around this longitude should induce a significant deceleration by days 4 and 5. The track guidance is in excellent agreement through the first 2 days, with less-than-typical spread beyond that time. The new track forecast is faster and adjusted slightly southward and then westward after day 3, but not as far south or west as the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 13.3N 127.5W 120 KT 140 MPH 12H 30/1200Z 13.9N 129.3W 115 KT 130 MPH 24H 31/0000Z 14.7N 131.8W 110 KT 125 MPH 36H 31/1200Z 15.4N 134.4W 110 KT 125 MPH 48H 01/0000Z 16.0N 136.7W 105 KT 120 MPH 72H 02/0000Z 16.9N 139.9W 95 KT 110 MPH 96H 03/0000Z 17.6N 141.9W 85 KT 100 MPH 120H 04/0000Z 18.1N 143.4W 75 KT 85 MPH $$ Forecaster Kimberlain

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Hurricane JIMENA Forecast Discussion Number 13

2015-08-29 22:32:53| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SAT AUG 29 2015 000 WTPZ43 KNHC 292032 TCDEP3 HURRICANE JIMENA DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 200 PM PDT SAT AUG 29 2015 Recent microwave imagery continued to show Jimena's eyewall nearly enclosed by a larger outer ring of convection, signaling that concentric eyewalls may be developing. A moat region is also evident in the latest visible images. Cloud tops have gradually warmed since this morning, and Jimena appears to have weakened a little. The initial intensity is set at 120 kt based on a blend of CI numbers of 6.0/115 from TAFB, 6.5/127 kt from SAB, and 6.3/122 kt from the CIMSS ADT. Jimena may be in the early stages of an eyewall replacement, which makes the short-term intensity forecast a little tricky. The overall environment remains conducive for strengthening, so if an eyewall replacement occurs, the hurricane has an opportunity to re-intensify during the next day or so. The bottom line is that fluctuations in intensity are likely during the next 24-48 hours, and Jimena is expected to remain a major hurricane during that time. After 48 hours, gradual weakening is indicated in the forecast, with the most likely reason being lower oceanic heat content. The hurricane models continue to show a much faster weakening rate than the global models, and as a compromise, the updated NHC intensity forecast lies near the upper end of the typically skillful models. This solution is closest to the SHIPS model. Jimena has turned west-northwestward with an initial motion of 285/8 kt. The subtropical ridge north of the hurricane is weakening, and Jimena is expected to continue moving toward the west-northwest through day 5. However, the cyclone should slow down considerably by days 4 and 5 due to weakening steering currents. The track guidance has continued to trend faster, and the updated NHC track forecast is again a little bit ahead of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 12.8N 126.4W 120 KT 140 MPH 12H 30/0600Z 13.4N 128.1W 125 KT 145 MPH 24H 30/1800Z 14.2N 130.4W 120 KT 140 MPH 36H 31/0600Z 15.0N 133.0W 115 KT 130 MPH 48H 31/1800Z 15.6N 135.4W 110 KT 125 MPH 72H 01/1800Z 16.6N 139.1W 105 KT 120 MPH 96H 02/1800Z 17.4N 141.3W 95 KT 110 MPH 120H 03/1800Z 18.0N 142.7W 85 KT 100 MPH $$ Forecaster Berg

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Hurricane JIMENA Forecast Discussion Number 12

2015-08-29 16:34:19| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SAT AUG 29 2015 000 WTPZ43 KNHC 291434 TCDEP3 HURRICANE JIMENA DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 800 AM PDT SAT AUG 29 2015 Convective cloud tops in the central dense overcast have warmed since the last advisory, but the 10-15 n mi wide eye remains distinct. An 0913 UTC GCOM overpass clearly indicated that the formation of a secondary outer eyewall was almost complete, which could be a harbinger that Jimena will soon go through an eyewall replacement. Dvorak Current Intensity estimates at 1200 UTC were 6.0/115 kt from TAFB, 6.5/127 kt from SAB, and 6.8/135 kt from the CIMSS ADT, and the initial intensity is held at 130 kt. This advisory continues to show the possibility of Jimena reaching category 5 intensity during the next 24 hours since the environment remains conducive for strengthening. However, if Jimena does go through an eyewall replacement soon, then fluctuations in intensity are likely to occur, and the hurricane could actually weaken a bit in the short term. The intensity forecast is somewhat challenging after 24 hours. Vertical shear is expected to remain low, and sea surface temperatures remain above 26C through the forecast period, but the hurricane models show a general decay to a category 1 or 2 cyclone by day 5. On the other hand, the global models, particularly the GFS and ECMWF, seem to take more advantage of the favorable environment and retain central pressures that would support a category 3 or 4 hurricane through day 5. Therefore, the NHC intensity forecast shows a much slower decay than indicated by the hurricane models, keeping Jimena as a major hurricane through day 4. Jimena's eye has been wobbling around, but the longer-term motion estimate is 275/7 kt. The ridge to the north of the hurricane appears to be weakening, and Jimena is expected to turn west-northwestward later today. This trajectory should continue through day 5, with a decrease in forward speed by days 4 and 5 when the steering currents become much weaker. The track guidance is still in good agreement on the future track, and the updated NHC forecast is similar to, but slightly faster than, the previous forecast after 24 hours. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 12.5N 125.6W 130 KT 150 MPH 12H 30/0000Z 13.0N 127.0W 135 KT 155 MPH 24H 30/1200Z 13.9N 129.1W 140 KT 160 MPH 36H 31/0000Z 14.7N 131.5W 135 KT 155 MPH 48H 31/1200Z 15.4N 133.9W 130 KT 150 MPH 72H 01/1200Z 16.5N 137.9W 115 KT 130 MPH 96H 02/1200Z 17.1N 140.5W 100 KT 115 MPH 120H 03/1200Z 17.6N 142.1W 90 KT 105 MPH $$ Forecaster Berg

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Remnants of ERIKA Forecast Discussion Number 19

2015-08-29 15:31:17| National Hurricane Center (Atlantic)

Issued at 930 AM EDT SAT AUG 29 2015 000 WTNT45 KNHC 291331 TCDAT5 REMNANTS OF ERIKA SPECIAL DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 930 AM EDT SAT AUG 29 2015 Surface observations from Cuba, satellite imagery, and reports from an Air Force Reserve Hurricane Hunter aircraft indicate that Erika has degenerated into a trough of low pressure, with the remnants of the center located near the north coast of eastern Cuba. Winds of near 30 kt are occurring to the north and east of the center, and these conditions will likely continue through at least this afternoon. The remnants are expected to move west-northwestward near the northern coast of central and eastern Cuba for the next 12 to 24 hours and reach the southeastern Gulf of Mexico in about 36 hours. After that time, a more northward motion is expected over the eastern Gulf of Mexico. The dynamical models suggests that the current strong wind shear could relax by the time the system reachs the Gulf of Mexico, and there is a possibility that Erika could regenerate. Regardless of regeneration, locally heavy rains and gusty winds should spread across portions of Cuba, the Bahamas, and southern Florida during the next couple of days. This will be the last advisory on this system by the National Hurricane Center unless regeneration occurs. Additional information can be found in the Tropical Weather Outlook issued by the National Hurricane Center, as well as marine forecasts and local forecast office products issued by the National Weather Service. FORECAST POSITIONS AND MAX WINDS INIT 29/1330Z 21.5N 75.9W 30 KT 35 MPH...REMNANTS 12H 29/1800Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm ERIKA Forecast Discussion Number 18

2015-08-29 10:54:19| National Hurricane Center (Atlantic)

Issued at 500 AM EDT SAT AUG 29 2015 000 WTNT45 KNHC 290854 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 AM EDT SAT AUG 29 2015 Erika remains very disorganized with the deep convection still displaced well east and southeast of the apparent center. The initial intensity has been set at 35 kt based on the latest Dvorak classification from TAFB, and these winds are likely occurring well east and northeast of the center. Erika will have to contend with land interaction and strong shear for the next day or so, which should result in the cyclone weakening to a depression later today, if not dissipating entirely. Assuming Erika survives the next 24 hours, some restrengthening is possible over the Gulf of Mexico in a less hostile environment. The low-confidence NHC intensity forecast is similar to the previous one and below the latest intensity consensus. The disorganized center of Erika has been difficult to locate, but my best estimate of the initial motion is 290/17, with the center moving a little to the left of the previous forecast track. Erika should gradually turn toward the northwest and decelerate during the next 36 to 48 hours as it moves around the edge of the subtropical ridge. After that time a northward motion at an even slower forward speed is expected. The new NHC track has been adjusted to the left, especially during the first 48 hours, due to the initial position and motion, and is largely an update of the previous forecast after that time. The NHC forecast is close to the multi-model consensus through 48 hours and is between the consensus and the GFS model after that time. Given the uncertainty in the initial position and motion, and whether Erika even has a closed center, confidence in the details of the track forecast remains low. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of Hispaniola and eastern Cuba. These rains could produce flash floods and mudslides. Although this would normally be an appropriate time for a tropical storm watch for portions of southern Florida following typical timelines, we have elected to wait until later today to see if the circulation of Erika has survived its interaction with Hispaniola. An Air Force Reserve Hurricane Hunter aircraft will be investigating Erika later this morning. There is a significant chance that no watches or warnings for Florida will be required. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 19.1N 75.1W 35 KT 40 MPH 12H 29/1800Z 20.3N 77.5W 30 KT 35 MPH 24H 30/0600Z 22.3N 80.3W 30 KT 35 MPH...INLAND 36H 30/1800Z 24.0N 82.1W 30 KT 35 MPH...OVER WATER 48H 31/0600Z 25.3N 83.2W 35 KT 40 MPH 72H 01/0600Z 27.0N 84.0W 35 KT 40 MPH 96H 02/0600Z 29.5N 84.5W 40 KT 45 MPH 120H 03/0600Z 31.0N 84.5W 25 KT 30 MPH...INLAND $$ Forecaster Brennan

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