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Tropical Storm ERIKA Forecast Discussion Number 15

2015-08-28 16:52:11| National Hurricane Center (Atlantic)

Issued at 1100 AM AST FRI AUG 28 2015 000 WTNT45 KNHC 281452 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 AM AST FRI AUG 28 2015 Morning visible imagery shows that the broad low-level center of Erika is exposed to the west of the main convective area due to the effects of 20-25 kt of westerly vertical wind shear. An Air Force Reserve Hurricane Hunter aircraft has reported a large area of 40-45 kt surface wind estimates from the Stepped Frequency Microwave Radiometer and 850 mb flight-level winds as high as 55 kt, so the initial intensity remains 45 kt. The central pressure based on the aircraft reports is 1008 mb. Now that the center is somewhat easier to locate, the initial motion is a somewhat more confident 285/16. A generally west-northwestward motion is expected for the next 48 hours or so as Erika moves around the southwestern periphery of the subtropical ridge. After that time, a northwestward and northward turn and a decrease in forward speed are forecast as Erika moves between the ridge and a mid- to upper-level trough over the Gulf of Mexico. The track guidance continues to show some spread based on the forecast strength of Erika. The models with a stronger cyclone, such as the GFDL and GFS, show a faster northward turn and are on the eastern side of the guidance envelope. On the other hand, the ECMWF forecasts a weaker storm and lies on the left side of the envelope. An extra complication is that passage over Hispaniola is likely to disrupt the circulation, with the possibility that the center could reform somewhere northwest or west of the island. Overall, the guidance envelope has shifted a little to the west since the previous advisory, and the new forecast track shows a similar nudge through 96 hours. The guidance is also showing a faster forward speed than six hours ago, so the new track is also a little faster than the previous track. Westerly to southwesterly vertical wind shear is forecast to continue or increase during the next 12 to 24 hours. This, combined with land interaction, suggests that the cyclone should weaken, and there is a chance the system could degenerate to a tropical wave while crossing Hispaniola. Assuming the cyclone survives, the shear should decrease some after 36 hours, which could allow some strengthening up to the time of possible landfall on the Florida Peninsula. The new intensity forecast is an update of the previous forecast, and like the previous forecast it is low confidence. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of the Dominican Republic and Haiti today and tonight. These rains could produce flash floods and mud slides. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 17.7N 69.4W 45 KT 50 MPH 12H 29/0000Z 19.3N 71.4W 40 KT 45 MPH...INLAND 24H 29/1200Z 20.8N 74.5W 40 KT 45 MPH...OVER WATER 36H 30/0000Z 22.3N 77.3W 40 KT 45 MPH 48H 30/1200Z 23.5N 79.2W 45 KT 50 MPH 72H 31/1200Z 26.0N 81.5W 50 KT 60 MPH...INLAND 96H 01/1200Z 28.5N 82.0W 40 KT 45 MPH...INLAND 120H 02/1200Z 30.5N 82.0W 35 KT 40 MPH...INLAND $$ Forecaster Beven

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Hurricane JIMENA Forecast Discussion Number 8

2015-08-28 16:32:14| National Hurricane Center (East Pacific)

Issued at 800 AM PDT FRI AUG 28 2015 000 WTPZ43 KNHC 281432 TCDEP3 HURRICANE JIMENA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 800 AM PDT FRI AUG 28 2015 Rapid intensification of Jimena continues this morning. Microwave data has shown an eye beneath the central dense overcast, and a more definitive eye is just now becoming apparent in infrared satellite imagery. With subjective Dvorak estimates of T4.5/77 kt from TAFB and SAB, and an objective estimate of T4.6/80 kt from UW-CIMSS, Jimena's initial intensity is raised to 80 kt. Jimena is expected to remain in an environment of low shear and over warm water for the duration of the forecast period. Mid-level moisture is high at the moment and is expected to only gradually decrease during the next 2 to 3 days. The SHIPS Rapid Intensification Index (RII) is showing a 54 percent chance of a 30-kt increase in intensity during the next 24 hours. Therefore, a continuation of RI appears likely and is explicitly shown in the NHC intensity forecast. A peak intensity is expected in about 48 hours, followed by gradual weakening through day 5 due to a slightly drier environment and lower oceanic heat content values. The updated NHC intensity forecast is generally a blend of the previous forecast with the latest SHIPS and LGEM guidance. It should be noted that once Jimena reaches its peak as a major hurricane, fluctuations in intensity that deviate from the official forecast are likely due to possible eyewall replacements. Jimena appears to have slowed down a bit, and the initial motion is 270/10 kt. The hurricane remains to the south of an anomalously strong ridge that extends southwestward from the southwestern United States, and this feature is expected to keep Jimena on a westward course for the next 24 hours. After that time, the ridge is expected to weaken, which will allow Jimena to turn west-northwestward through day 5. The track guidance remains in good agreement and very close to the previous forecast. Therefore, no significant changes are noted in the updated NHC track forecast. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 12.4N 122.0W 80 KT 90 MPH 12H 29/0000Z 12.4N 123.6W 95 KT 110 MPH 24H 29/1200Z 12.6N 125.5W 110 KT 125 MPH 36H 30/0000Z 13.2N 127.3W 120 KT 140 MPH 48H 30/1200Z 14.1N 129.2W 125 KT 145 MPH 72H 31/1200Z 15.9N 133.9W 120 KT 140 MPH 96H 01/1200Z 17.0N 138.0W 105 KT 120 MPH 120H 02/1200Z 17.5N 140.5W 90 KT 105 MPH $$ Forecaster Berg

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Tropical Storm ERIKA Forecast Discussion Number 14

2015-08-28 10:50:11| National Hurricane Center (Atlantic)

Issued at 500 AM AST FRI AUG 28 2015 000 WTNT45 KNHC 280850 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 AM AST FRI AUG 28 2015 Erika remains disorganized, with the deep convection decreasing in coverage and intensity to the east of the estimated center position during the past few hours. Despite this, the cyclone continues to produce a large area of tropical storm force winds east of the center, and the initial intensity of 45 kt and central pressure of 1006 mb are based on recent surface observations from Puerto Rico. The center of Erika continues to be rather disorganized, and the initial position and motion of 290/15 are based on a blend of satellite imagery and continuity. While the overall track forecast reasoning has not changed, the initial position and motion and an overall weaker depiction of Erika in the global models have resulted in a leftward shift in the track guidance this cycle and an increase in the forward speed. A west-northwestward motion is expected for the first couple of days as Erika moves around the southern periphery of the subtropical ridge to the north. After that time, a northwestward and northward turn and a decrease in forward speed are forecast as Erika moves around the western edge of the ridge. The new NHC track is to the left of and faster than the previous advisory and is near the multi model consensus through 36 hours. After that time, the NHC track is east of almost all the guidance out of respect to continuity. Needless to say, confidence in the track forecast, especially after 48 hours, remains very low given that the details of the track depend on how much the cyclone recovers from the shear and the effects of land interaction in the short term. Strong shear is expected to continue or even increase during the next day or so. The combination of the shear and interaction with Hispaniola suggests that Erika is likely to weaken and could even dissipate in the next 12 to 24 hours. Assuming that the cyclone survives, there is an opportunity for some intensification on days 2 and 3 of the forecast period as the shear decreases, and that is reflected in the NHC forecast. After that time, since the NHC track now takes Erika inland over the Florida peninsula, weakening is shown at days 4 and 5. Much of the guidance has trended weaker this cycle, and the NHC intensity forecast is close to the HWRF and the IVCN consensus. Confidence in the intensity forecast remains very low. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of the the Virgin Islands, Puerto Rico, the Dominican Republic, and Haiti today. These rains could produce flash floods and mud slides. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 17.7N 67.7W 45 KT 50 MPH 12H 28/1800Z 18.8N 69.8W 40 KT 45 MPH...INLAND 24H 29/0600Z 20.5N 72.9W 40 KT 45 MPH...OVER WATER 36H 29/1800Z 22.0N 76.0W 40 KT 45 MPH 48H 30/0600Z 23.2N 78.1W 45 KT 50 MPH 72H 31/0600Z 25.6N 80.7W 50 KT 60 MPH...INLAND 96H 01/0600Z 27.7N 81.6W 45 KT 50 MPH...INLAND 120H 02/0600Z 30.0N 82.0W 40 KT 45 MPH...INLAND $$ Forecaster Brennan

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Tropical Storm ERIKA Forecast Discussion Number 13

2015-08-28 05:04:10| National Hurricane Center (Atlantic)

Issued at 1100 PM AST THU AUG 27 2015 000 WTNT45 KNHC 280304 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 PM AST THU AUG 27 2015 The center of Erika is not easy to locate tonight, and it appears that a few smaller swirls are rotating within a larger gyre. In fact, one of these small swirls moved near St. Croix producing tropical storm force wind gusts during the past few hours on the island. Due to the lack of an inner core, the initial position is based on a mean center of circulation. Despite the poor organization, the reconnaissance plane currently in Erika was able to measure 700 mb flight-level winds of 59 kt well to the southeast of the alleged center. Based on the SFMR, these winds are not at the surface, and the initial intensity is kept at 40 kt. The central pressure is not falling, which is another indication that Erika is not strengthening. The NHC forecast calls for no change in intensity during the next 36 hours, given the fact that cyclone will be moving through a very hostile shear environment, and will also feel the effects of land. Once in the Bahamas, however, the upper-level flow is expected to become more favorable, and if Erika survives, it has the opportunity to strengthen some. The NHC forecast is very close to the intensity consensus and is similar to the previous one. The best estimate of the initial motion is toward the west or 270 degrees at 15 kt, and this estimate is highly uncertain. Erika should begin to turn toward the west-northwest during the next several hours around the periphery of the western Atlantic subtropical ridge, and should reach the Central Bahamas between 36 and 48 hours. By then, the cyclone will be located on the southwestern edge of the ridge, and should begin to turn to the northwest with decreasing forward speed. Most of the track guidance, including the ECMWF and the GFS global models, show a tropical cyclone approaching southeast Florida in about 3 days and moving northward near or over the east coast of Florida during the latter portion of the forecast period. There is unusually high uncertainty in this forecast, especially at days 3 to 5, given that the cyclone has to recover from shear and from the effects of land for this to occur. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of the northern Leeward Islands tonight, and over the Virgin Islands and Puerto Rico on Friday. These rains could produce flash floods and mud slides. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 16.6N 65.3W 40 KT 45 MPH 12H 28/1200Z 18.2N 67.4W 40 KT 45 MPH 24H 29/0000Z 19.7N 70.2W 40 KT 45 MPH 36H 29/1200Z 21.1N 73.2W 40 KT 45 MPH 48H 30/0000Z 22.5N 75.5W 45 KT 50 MPH 72H 31/0000Z 25.2N 79.0W 55 KT 65 MPH 96H 01/0000Z 27.3N 80.2W 65 KT 75 MPH 120H 02/0000Z 29.5N 80.7W 75 KT 85 MPH $$ Forecaster Avila

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Tropical Storm JIMENA Forecast Discussion Number 6

2015-08-28 04:55:09| National Hurricane Center (East Pacific)

Issued at 800 PM PDT THU AUG 27 2015 000 WTPZ43 KNHC 280255 TCDEP3 TROPICAL STORM JIMENA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 800 PM PDT THU AUG 27 2015 Jimena has continued to rapidly intensify. Several convective bands are tightly coiled and wrapping into the center where a small central dense overcast feature has developed during the past couple of hours. Upper-level outflow is nearly symmetrical and continues to expand. The initial intensity of 60 kt is based on a blend of consensus Dvorak satellite intensity estimates of T3.5/55 kt from TAFB and SAB, and a UW-CIMSS ADT value of T3.9/63 kt. The initial motion estimate is 270/12 kt. There is no significant change to the previous track forecast or reasoning. The NHC model guidance is tightly packed about the previous forecast track, and Jimena is expected to move westward along the southern periphery of a strong subtropical ridge for the next 36-48 hours. After that time, a turn toward the west-northwest accompanied by a decrease in forward speed is expected as a mid-latitude trough digs southward along 130-135W longitude, weakening the ridge and the steering currents. The new forecast track is essentially just an extension of the previous advisory track. Jimena has been rapidly intensifying for the past 24 hours, so the question now is how long will Jimena continue this develop trend. The surrounding atmospheric and oceanic environments are quite conducive for additional strengthening. Recent SSMI and SSMI/S microwave satellite images indicate that a nearly closed eye of 15-20 nmi diameter has formed in the low- and mid-levels, which favors continued rapid strengthening. Those same images also indicated that dry mid-level air had wrapped into the northern semicircle and had penetrated the inner-core convective region, which could hinder development. However, this hindering factor should be short lived given the very robust circulation noted in conventional satellite imagery, which should quickly mix out any dry. air intrusions. Therefore, since the vertical wind shear is forecast to remain less than 10 kt, rapid intensification is forecast to continue for another 36 hours or so. After that time, the expected intense circulation of Jimena should begin to create cold upwelling since the cyclone will be moving over significantly lower upper ocean heat content values, which should cap the intensification process and induce slow weakening by days 4 and 5. The official intensity forecast is similar to the previous advisory, and lies between the forecasts of the SHIPS and LGEM models, which have performed quite well thus far with Jimena. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 12.3N 119.9W 60 KT 70 MPH 12H 28/1200Z 12.3N 121.7W 75 KT 85 MPH 24H 29/0000Z 12.4N 123.7W 90 KT 105 MPH 36H 29/1200Z 12.6N 125.6W 105 KT 120 MPH 48H 30/0000Z 13.2N 127.3W 110 KT 125 MPH 72H 31/0000Z 14.8N 131.7W 125 KT 145 MPH 96H 01/0000Z 16.5N 136.0W 120 KT 140 MPH 120H 02/0000Z 17.5N 139.0W 110 KT 125 MPH $$ Forecaster Stewart

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